linux-stable/drivers/gpu/drm/i915/intel_ringbuffer.h

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#ifndef _INTEL_RINGBUFFER_H_
#define _INTEL_RINGBUFFER_H_
#include <linux/hashtable.h>
#include "i915_gem_batch_pool.h"
#define I915_CMD_HASH_ORDER 9
/* Early gen2 devices have a cacheline of just 32 bytes, using 64 is overkill,
* but keeps the logic simple. Indeed, the whole purpose of this macro is just
* to give some inclination as to some of the magic values used in the various
* workarounds!
*/
#define CACHELINE_BYTES 64
/*
* Gen2 BSpec "1. Programming Environment" / 1.4.4.6 "Ring Buffer Use"
* Gen3 BSpec "vol1c Memory Interface Functions" / 2.3.4.5 "Ring Buffer Use"
* Gen4+ BSpec "vol1c Memory Interface and Command Stream" / 5.3.4.5 "Ring Buffer Use"
*
* "If the Ring Buffer Head Pointer and the Tail Pointer are on the same
* cacheline, the Head Pointer must not be greater than the Tail
* Pointer."
*/
#define I915_RING_FREE_SPACE 64
struct intel_hw_status_page {
u32 *page_addr;
unsigned int gfx_addr;
struct drm_i915_gem_object *obj;
};
#define I915_READ_TAIL(ring) I915_READ(RING_TAIL((ring)->mmio_base))
#define I915_WRITE_TAIL(ring, val) I915_WRITE(RING_TAIL((ring)->mmio_base), val)
#define I915_READ_START(ring) I915_READ(RING_START((ring)->mmio_base))
#define I915_WRITE_START(ring, val) I915_WRITE(RING_START((ring)->mmio_base), val)
#define I915_READ_HEAD(ring) I915_READ(RING_HEAD((ring)->mmio_base))
#define I915_WRITE_HEAD(ring, val) I915_WRITE(RING_HEAD((ring)->mmio_base), val)
#define I915_READ_CTL(ring) I915_READ(RING_CTL((ring)->mmio_base))
#define I915_WRITE_CTL(ring, val) I915_WRITE(RING_CTL((ring)->mmio_base), val)
#define I915_READ_IMR(ring) I915_READ(RING_IMR((ring)->mmio_base))
#define I915_WRITE_IMR(ring, val) I915_WRITE(RING_IMR((ring)->mmio_base), val)
#define I915_READ_MODE(ring) I915_READ(RING_MI_MODE((ring)->mmio_base))
#define I915_WRITE_MODE(ring, val) I915_WRITE(RING_MI_MODE((ring)->mmio_base), val)
/* seqno size is actually only a uint32, but since we plan to use MI_FLUSH_DW to
* do the writes, and that must have qw aligned offsets, simply pretend it's 8b.
*/
#define i915_semaphore_seqno_size sizeof(uint64_t)
#define GEN8_SIGNAL_OFFSET(__ring, to) \
(i915_gem_obj_ggtt_offset(dev_priv->semaphore_obj) + \
((__ring)->id * I915_NUM_RINGS * i915_semaphore_seqno_size) + \
(i915_semaphore_seqno_size * (to)))
#define GEN8_WAIT_OFFSET(__ring, from) \
(i915_gem_obj_ggtt_offset(dev_priv->semaphore_obj) + \
((from) * I915_NUM_RINGS * i915_semaphore_seqno_size) + \
(i915_semaphore_seqno_size * (__ring)->id))
#define GEN8_RING_SEMAPHORE_INIT do { \
if (!dev_priv->semaphore_obj) { \
break; \
} \
ring->semaphore.signal_ggtt[RCS] = GEN8_SIGNAL_OFFSET(ring, RCS); \
ring->semaphore.signal_ggtt[VCS] = GEN8_SIGNAL_OFFSET(ring, VCS); \
ring->semaphore.signal_ggtt[BCS] = GEN8_SIGNAL_OFFSET(ring, BCS); \
ring->semaphore.signal_ggtt[VECS] = GEN8_SIGNAL_OFFSET(ring, VECS); \
ring->semaphore.signal_ggtt[VCS2] = GEN8_SIGNAL_OFFSET(ring, VCS2); \
ring->semaphore.signal_ggtt[ring->id] = MI_SEMAPHORE_SYNC_INVALID; \
} while(0)
enum intel_ring_hangcheck_action {
HANGCHECK_IDLE = 0,
HANGCHECK_WAIT,
HANGCHECK_ACTIVE,
HANGCHECK_ACTIVE_LOOP,
HANGCHECK_KICK,
HANGCHECK_HUNG,
};
#define HANGCHECK_SCORE_RING_HUNG 31
struct intel_ring_hangcheck {
u64 acthd;
u64 max_acthd;
u32 seqno;
drm/i915: detect hang using per ring hangcheck_score Keep track of ring seqno progress and if there are no progress detected, declare hang. Use actual head (acthd) to distinguish between ring stuck and batchbuffer looping situation. Stuck ring will be kicked to trigger progress. This commit adds a hard limit for batchbuffer completion time. If batchbuffer completion time is more than 4.5 seconds, the gpu will be declared hung. Review comment from Ben which nicely clarifies the semantic change: "Maybe I'm just stating the functional changes of the patch, but in case they were unintended here is what I see as potential issues: 1. "If ring B is waiting on ring A via semaphore, and ring A is making progress, albeit slowly - the hangcheck will fire. The check will determine that A is moving, however ring B will appear hung because the ACTHD doesn't move. I honestly can't say if that's actually a realistic problem to hit it probably implies the timeout value is too low. 2. "There's also another corner case on the kick. If the seqno = 2 (though not stuck), and on the 3rd hangcheck, the ring is stuck, and we try to kick it... we don't actually try to find out if the kick helped" v2: use atchd to detect stuck ring from loop (Ben Widawsky) v3: Use acthd to check when ring needs kicking. Declare hang on third time in order to give time for kick_ring to take effect. v4: Update commit msg Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com> Reviewed-by: Ben Widawsky <ben@bwidawsk.net> [danvet: Paste in Ben's review comment.] Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2013-05-30 06:04:29 +00:00
int score;
enum intel_ring_hangcheck_action action;
int deadlock;
};
struct intel_ringbuffer {
struct drm_i915_gem_object *obj;
void __iomem *virtual_start;
struct intel_engine_cs *ring;
u32 head;
u32 tail;
int space;
int size;
int effective_size;
/** We track the position of the requests in the ring buffer, and
* when each is retired we increment last_retired_head as the GPU
* must have finished processing the request and so we know we
* can advance the ringbuffer up to that position.
*
* last_retired_head is set to -1 after the value is consumed so
* we can detect new retirements.
*/
u32 last_retired_head;
};
struct intel_context;
struct drm_i915_reg_descriptor;
struct intel_engine_cs {
const char *name;
enum intel_ring_id {
RCS = 0x0,
VCS,
BCS,
VECS,
VCS2
} id;
#define I915_NUM_RINGS 5
#define LAST_USER_RING (VECS + 1)
u32 mmio_base;
struct drm_device *dev;
struct intel_ringbuffer *buffer;
/*
* A pool of objects to use as shadow copies of client batch buffers
* when the command parser is enabled. Prevents the client from
* modifying the batch contents after software parsing.
*/
struct i915_gem_batch_pool batch_pool;
struct intel_hw_status_page status_page;
unsigned irq_refcount; /* protected by dev_priv->irq_lock */
u32 irq_enable_mask; /* bitmask to enable ring interrupt */
struct drm_i915_gem_request *trace_irq_req;
bool __must_check (*irq_get)(struct intel_engine_cs *ring);
void (*irq_put)(struct intel_engine_cs *ring);
int (*init_hw)(struct intel_engine_cs *ring);
int (*init_context)(struct intel_engine_cs *ring,
struct intel_context *ctx);
void (*write_tail)(struct intel_engine_cs *ring,
u32 value);
int __must_check (*flush)(struct intel_engine_cs *ring,
u32 invalidate_domains,
u32 flush_domains);
int (*add_request)(struct intel_engine_cs *ring);
/* Some chipsets are not quite as coherent as advertised and need
* an expensive kick to force a true read of the up-to-date seqno.
* However, the up-to-date seqno is not always required and the last
* seen value is good enough. Note that the seqno will always be
* monotonic, even if not coherent.
*/
u32 (*get_seqno)(struct intel_engine_cs *ring,
bool lazy_coherency);
void (*set_seqno)(struct intel_engine_cs *ring,
u32 seqno);
int (*dispatch_execbuffer)(struct intel_engine_cs *ring,
u64 offset, u32 length,
unsigned dispatch_flags);
#define I915_DISPATCH_SECURE 0x1
#define I915_DISPATCH_PINNED 0x2
void (*cleanup)(struct intel_engine_cs *ring);
/* GEN8 signal/wait table - never trust comments!
* signal to signal to signal to signal to signal to
* RCS VCS BCS VECS VCS2
* --------------------------------------------------------------------
* RCS | NOP (0x00) | VCS (0x08) | BCS (0x10) | VECS (0x18) | VCS2 (0x20) |
* |-------------------------------------------------------------------
* VCS | RCS (0x28) | NOP (0x30) | BCS (0x38) | VECS (0x40) | VCS2 (0x48) |
* |-------------------------------------------------------------------
* BCS | RCS (0x50) | VCS (0x58) | NOP (0x60) | VECS (0x68) | VCS2 (0x70) |
* |-------------------------------------------------------------------
* VECS | RCS (0x78) | VCS (0x80) | BCS (0x88) | NOP (0x90) | VCS2 (0x98) |
* |-------------------------------------------------------------------
* VCS2 | RCS (0xa0) | VCS (0xa8) | BCS (0xb0) | VECS (0xb8) | NOP (0xc0) |
* |-------------------------------------------------------------------
*
* Generalization:
* f(x, y) := (x->id * NUM_RINGS * seqno_size) + (seqno_size * y->id)
* ie. transpose of g(x, y)
*
* sync from sync from sync from sync from sync from
* RCS VCS BCS VECS VCS2
* --------------------------------------------------------------------
* RCS | NOP (0x00) | VCS (0x28) | BCS (0x50) | VECS (0x78) | VCS2 (0xa0) |
* |-------------------------------------------------------------------
* VCS | RCS (0x08) | NOP (0x30) | BCS (0x58) | VECS (0x80) | VCS2 (0xa8) |
* |-------------------------------------------------------------------
* BCS | RCS (0x10) | VCS (0x38) | NOP (0x60) | VECS (0x88) | VCS2 (0xb0) |
* |-------------------------------------------------------------------
* VECS | RCS (0x18) | VCS (0x40) | BCS (0x68) | NOP (0x90) | VCS2 (0xb8) |
* |-------------------------------------------------------------------
* VCS2 | RCS (0x20) | VCS (0x48) | BCS (0x70) | VECS (0x98) | NOP (0xc0) |
* |-------------------------------------------------------------------
*
* Generalization:
* g(x, y) := (y->id * NUM_RINGS * seqno_size) + (seqno_size * x->id)
* ie. transpose of f(x, y)
*/
struct {
u32 sync_seqno[I915_NUM_RINGS-1];
union {
struct {
/* our mbox written by others */
u32 wait[I915_NUM_RINGS];
/* mboxes this ring signals to */
u32 signal[I915_NUM_RINGS];
} mbox;
u64 signal_ggtt[I915_NUM_RINGS];
};
/* AKA wait() */
int (*sync_to)(struct intel_engine_cs *ring,
struct intel_engine_cs *to,
u32 seqno);
int (*signal)(struct intel_engine_cs *signaller,
/* num_dwords needed by caller */
unsigned int num_dwords);
} semaphore;
/* Execlists */
spinlock_t execlist_lock;
struct list_head execlist_queue;
struct list_head execlist_retired_req_list;
2014-07-24 16:04:39 +00:00
u8 next_context_status_buffer;
u32 irq_keep_mask; /* bitmask for interrupts that should not be masked */
int (*emit_request)(struct intel_ringbuffer *ringbuf,
struct drm_i915_gem_request *request);
int (*emit_flush)(struct intel_ringbuffer *ringbuf,
struct intel_context *ctx,
u32 invalidate_domains,
u32 flush_domains);
int (*emit_bb_start)(struct intel_ringbuffer *ringbuf,
struct intel_context *ctx,
u64 offset, unsigned dispatch_flags);
/**
* List of objects currently involved in rendering from the
* ringbuffer.
*
* Includes buffers having the contents of their GPU caches
* flushed, not necessarily primitives. last_read_req
* represents when the rendering involved will be completed.
*
* A reference is held on the buffer while on this list.
*/
struct list_head active_list;
/**
* List of breadcrumbs associated with GPU requests currently
* outstanding.
*/
struct list_head request_list;
/**
* Do we have some not yet emitted requests outstanding?
*/
struct drm_i915_gem_request *outstanding_lazy_request;
2012-06-13 18:45:19 +00:00
bool gpu_caches_dirty;
wait_queue_head_t irq_queue;
struct intel_context *default_context;
struct intel_context *last_context;
struct intel_ring_hangcheck hangcheck;
struct {
struct drm_i915_gem_object *obj;
u32 gtt_offset;
volatile u32 *cpu_page;
} scratch;
bool needs_cmd_parser;
/*
* Table of commands the command parser needs to know about
* for this ring.
*/
DECLARE_HASHTABLE(cmd_hash, I915_CMD_HASH_ORDER);
/*
* Table of registers allowed in commands that read/write registers.
*/
const struct drm_i915_reg_descriptor *reg_table;
int reg_count;
/*
* Table of registers allowed in commands that read/write registers, but
* only from the DRM master.
*/
const struct drm_i915_reg_descriptor *master_reg_table;
int master_reg_count;
/*
* Returns the bitmask for the length field of the specified command.
* Return 0 for an unrecognized/invalid command.
*
* If the command parser finds an entry for a command in the ring's
* cmd_tables, it gets the command's length based on the table entry.
* If not, it calls this function to determine the per-ring length field
* encoding for the command (i.e. certain opcode ranges use certain bits
* to encode the command length in the header).
*/
u32 (*get_cmd_length_mask)(u32 cmd_header);
};
bool intel_ring_initialized(struct intel_engine_cs *ring);
static inline unsigned
intel_ring_flag(struct intel_engine_cs *ring)
{
return 1 << ring->id;
}
static inline u32
intel_ring_sync_index(struct intel_engine_cs *ring,
struct intel_engine_cs *other)
{
int idx;
/*
* rcs -> 0 = vcs, 1 = bcs, 2 = vecs, 3 = vcs2;
* vcs -> 0 = bcs, 1 = vecs, 2 = vcs2, 3 = rcs;
* bcs -> 0 = vecs, 1 = vcs2. 2 = rcs, 3 = vcs;
* vecs -> 0 = vcs2, 1 = rcs, 2 = vcs, 3 = bcs;
* vcs2 -> 0 = rcs, 1 = vcs, 2 = bcs, 3 = vecs;
*/
idx = (other - ring) - 1;
if (idx < 0)
idx += I915_NUM_RINGS;
return idx;
}
static inline u32
intel_read_status_page(struct intel_engine_cs *ring,
int reg)
{
/* Ensure that the compiler doesn't optimize away the load. */
barrier();
return ring->status_page.page_addr[reg];
}
static inline void
intel_write_status_page(struct intel_engine_cs *ring,
int reg, u32 value)
{
ring->status_page.page_addr[reg] = value;
}
/**
* Reads a dword out of the status page, which is written to from the command
* queue by automatic updates, MI_REPORT_HEAD, MI_STORE_DATA_INDEX, or
* MI_STORE_DATA_IMM.
*
* The following dwords have a reserved meaning:
* 0x00: ISR copy, updated when an ISR bit not set in the HWSTAM changes.
* 0x04: ring 0 head pointer
* 0x05: ring 1 head pointer (915-class)
* 0x06: ring 2 head pointer (915-class)
* 0x10-0x1b: Context status DWords (GM45)
* 0x1f: Last written status offset. (GM45)
* 0x20-0x2f: Reserved (Gen6+)
*
* The area from dword 0x30 to 0x3ff is available for driver usage.
*/
#define I915_GEM_HWS_INDEX 0x30
#define I915_GEM_HWS_SCRATCH_INDEX 0x40
#define I915_GEM_HWS_SCRATCH_ADDR (I915_GEM_HWS_SCRATCH_INDEX << MI_STORE_DWORD_INDEX_SHIFT)
drm/i915/bdw: Pin the ringbuffer backing object to GGTT on-demand Same as with the context, pinning to GGTT regardless is harmful (it badly fragments the GGTT and can even exhaust it). Unfortunately, this case is also more complex than the previous one because we need to map and access the ringbuffer in several places along the execbuffer path (and we cannot make do by leaving the default ringbuffer pinned, as before). Also, the context object itself contains a pointer to the ringbuffer address that we have to keep updated if we are going to allow the ringbuffer to move around. v2: Same as with the context pinning, we cannot really do it during an interrupt. Also, pin the default ringbuffers objects regardless (makes error capture a lot easier). v3: Rebased. Take a pin reference of the ringbuffer for each item in the execlist request queue because the hardware may still be using the ringbuffer after the MI_USER_INTERRUPT to notify the seqno update is executed. The ringbuffer must remain pinned until the context save is complete. No longer pin and unpin ringbuffer in populate_lr_context() - this transient address is meaningless and the pinning can cause a sleep while atomic. v4: Moved ringbuffer pin and unpin into the lr_context_pin functions. Downgraded pinning check BUG_ONs to WARN_ONs. v5: Reinstated WARN_ONs for unexpected execlist states. Removed unused variable. Issue: VIZ-4277 Signed-off-by: Oscar Mateo <oscar.mateo@intel.com> Signed-off-by: Thomas Daniel <thomas.daniel@intel.com> Reviewed-by: Akash Goel <akash.goels@gmail.com> Reviewed-by: Deepak S<deepak.s@linux.intel.com> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2014-11-13 10:28:56 +00:00
void intel_unpin_ringbuffer_obj(struct intel_ringbuffer *ringbuf);
int intel_pin_and_map_ringbuffer_obj(struct drm_device *dev,
struct intel_ringbuffer *ringbuf);
void intel_destroy_ringbuffer_obj(struct intel_ringbuffer *ringbuf);
int intel_alloc_ringbuffer_obj(struct drm_device *dev,
struct intel_ringbuffer *ringbuf);
void intel_stop_ring_buffer(struct intel_engine_cs *ring);
void intel_cleanup_ring_buffer(struct intel_engine_cs *ring);
int intel_ring_alloc_request_extras(struct drm_i915_gem_request *request);
int __must_check intel_ring_begin(struct intel_engine_cs *ring, int n);
int __must_check intel_ring_cacheline_align(struct intel_engine_cs *ring);
static inline void intel_ring_emit(struct intel_engine_cs *ring,
u32 data)
{
struct intel_ringbuffer *ringbuf = ring->buffer;
iowrite32(data, ringbuf->virtual_start + ringbuf->tail);
ringbuf->tail += 4;
}
static inline void intel_ring_advance(struct intel_engine_cs *ring)
drm/i915: Write RING_TAIL once per-request Ignoring the legacy DRI1 code, and a couple of special cases (to be discussed later), all access to the ring is mediated through requests. The first write to a ring will grab a seqno and mark the ring as having an outstanding_lazy_request. Either through explicitly adding a request after an execbuffer or through an implicit wait (either by the CPU or by a semaphore), that sequence of writes will be terminated with a request. So we can ellide all the intervening writes to the tail register and send the entire command stream to the GPU at once. This will reduce the number of *serialising* writes to the tail register by a factor or 3-5 times (depending upon architecture and number of workarounds, context switches, etc involved). This becomes even more noticeable when the register write is overloaded with a number of debugging tools. The astute reader will wonder if it is then possible to overflow the ring with a single command. It is not. When we start a command sequence to the ring, we check for available space and issue a wait in case we have not. The ring wait will in this case be forced to flush the outstanding register write and then poll the ACTHD for sufficient space to continue. The exception to the rule where everything is inside a request are a few initialisation cases where we may want to write GPU commands via the CS before userspace wakes up and page flips. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2013-08-10 21:16:32 +00:00
{
struct intel_ringbuffer *ringbuf = ring->buffer;
ringbuf->tail &= ringbuf->size - 1;
drm/i915: Write RING_TAIL once per-request Ignoring the legacy DRI1 code, and a couple of special cases (to be discussed later), all access to the ring is mediated through requests. The first write to a ring will grab a seqno and mark the ring as having an outstanding_lazy_request. Either through explicitly adding a request after an execbuffer or through an implicit wait (either by the CPU or by a semaphore), that sequence of writes will be terminated with a request. So we can ellide all the intervening writes to the tail register and send the entire command stream to the GPU at once. This will reduce the number of *serialising* writes to the tail register by a factor or 3-5 times (depending upon architecture and number of workarounds, context switches, etc involved). This becomes even more noticeable when the register write is overloaded with a number of debugging tools. The astute reader will wonder if it is then possible to overflow the ring with a single command. It is not. When we start a command sequence to the ring, we check for available space and issue a wait in case we have not. The ring wait will in this case be forced to flush the outstanding register write and then poll the ACTHD for sufficient space to continue. The exception to the rule where everything is inside a request are a few initialisation cases where we may want to write GPU commands via the CS before userspace wakes up and page flips. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2013-08-10 21:16:32 +00:00
}
int __intel_ring_space(int head, int tail, int size);
void intel_ring_update_space(struct intel_ringbuffer *ringbuf);
int intel_ring_space(struct intel_ringbuffer *ringbuf);
bool intel_ring_stopped(struct intel_engine_cs *ring);
void __intel_ring_advance(struct intel_engine_cs *ring);
drm/i915: Write RING_TAIL once per-request Ignoring the legacy DRI1 code, and a couple of special cases (to be discussed later), all access to the ring is mediated through requests. The first write to a ring will grab a seqno and mark the ring as having an outstanding_lazy_request. Either through explicitly adding a request after an execbuffer or through an implicit wait (either by the CPU or by a semaphore), that sequence of writes will be terminated with a request. So we can ellide all the intervening writes to the tail register and send the entire command stream to the GPU at once. This will reduce the number of *serialising* writes to the tail register by a factor or 3-5 times (depending upon architecture and number of workarounds, context switches, etc involved). This becomes even more noticeable when the register write is overloaded with a number of debugging tools. The astute reader will wonder if it is then possible to overflow the ring with a single command. It is not. When we start a command sequence to the ring, we check for available space and issue a wait in case we have not. The ring wait will in this case be forced to flush the outstanding register write and then poll the ACTHD for sufficient space to continue. The exception to the rule where everything is inside a request are a few initialisation cases where we may want to write GPU commands via the CS before userspace wakes up and page flips. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2013-08-10 21:16:32 +00:00
int __must_check intel_ring_idle(struct intel_engine_cs *ring);
void intel_ring_init_seqno(struct intel_engine_cs *ring, u32 seqno);
int intel_ring_flush_all_caches(struct intel_engine_cs *ring);
int intel_ring_invalidate_all_caches(struct intel_engine_cs *ring);
void intel_fini_pipe_control(struct intel_engine_cs *ring);
int intel_init_pipe_control(struct intel_engine_cs *ring);
int intel_init_render_ring_buffer(struct drm_device *dev);
int intel_init_bsd_ring_buffer(struct drm_device *dev);
int intel_init_bsd2_ring_buffer(struct drm_device *dev);
int intel_init_blt_ring_buffer(struct drm_device *dev);
int intel_init_vebox_ring_buffer(struct drm_device *dev);
u64 intel_ring_get_active_head(struct intel_engine_cs *ring);
int init_workarounds_ring(struct intel_engine_cs *ring);
static inline u32 intel_ring_get_tail(struct intel_ringbuffer *ringbuf)
drm/i915: Record the tail at each request and use it to estimate the head By recording the location of every request in the ringbuffer, we know that in order to retire the request the GPU must have finished reading it and so the GPU head is now beyond the tail of the request. We can therefore provide a conservative estimate of where the GPU is reading from in order to avoid having to read back the ring buffer registers when polling for space upon starting a new write into the ringbuffer. A secondary effect is that this allows us to convert intel_ring_buffer_wait() to use i915_wait_request() and so consolidate upon the single function to handle the complicated task of waiting upon the GPU. A necessary precaution is that we need to make that wait uninterruptible to match the existing conditions as all the callers of intel_ring_begin() have not been audited to handle ERESTARTSYS correctly. By using a conservative estimate for the head, and always processing all outstanding requests first, we prevent a race condition between using the estimate and direct reads of I915_RING_HEAD which could result in the value of the head going backwards, and the tail overflowing once again. We are also careful to mark any request that we skip over in order to free space in ring as consumed which provides a self-consistency check. Given sufficient abuse, such as a set of unthrottled GPU bound cairo-traces, avoiding the use of I915_RING_HEAD gives a 10-20% boost on Sandy Bridge (i5-2520m): firefox-paintball 18927ms -> 15646ms: 1.21x speedup firefox-fishtank 12563ms -> 11278ms: 1.11x speedup which is a mild consolation for the performance those traces achieved from exploiting the buggy autoreported head. v2: Add a few more comments and make request->tail a conservative estimate as suggested by Daniel Vetter. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> [danvet: resolve conflicts with retirement defering and the lack of the autoreport head removal (that will go in through -fixes).] Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2012-02-15 11:25:36 +00:00
{
return ringbuf->tail;
drm/i915: Record the tail at each request and use it to estimate the head By recording the location of every request in the ringbuffer, we know that in order to retire the request the GPU must have finished reading it and so the GPU head is now beyond the tail of the request. We can therefore provide a conservative estimate of where the GPU is reading from in order to avoid having to read back the ring buffer registers when polling for space upon starting a new write into the ringbuffer. A secondary effect is that this allows us to convert intel_ring_buffer_wait() to use i915_wait_request() and so consolidate upon the single function to handle the complicated task of waiting upon the GPU. A necessary precaution is that we need to make that wait uninterruptible to match the existing conditions as all the callers of intel_ring_begin() have not been audited to handle ERESTARTSYS correctly. By using a conservative estimate for the head, and always processing all outstanding requests first, we prevent a race condition between using the estimate and direct reads of I915_RING_HEAD which could result in the value of the head going backwards, and the tail overflowing once again. We are also careful to mark any request that we skip over in order to free space in ring as consumed which provides a self-consistency check. Given sufficient abuse, such as a set of unthrottled GPU bound cairo-traces, avoiding the use of I915_RING_HEAD gives a 10-20% boost on Sandy Bridge (i5-2520m): firefox-paintball 18927ms -> 15646ms: 1.21x speedup firefox-fishtank 12563ms -> 11278ms: 1.11x speedup which is a mild consolation for the performance those traces achieved from exploiting the buggy autoreported head. v2: Add a few more comments and make request->tail a conservative estimate as suggested by Daniel Vetter. Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk> [danvet: resolve conflicts with retirement defering and the lack of the autoreport head removal (that will go in through -fixes).] Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
2012-02-15 11:25:36 +00:00
}
static inline struct drm_i915_gem_request *
intel_ring_get_request(struct intel_engine_cs *ring)
{
BUG_ON(ring->outstanding_lazy_request == NULL);
return ring->outstanding_lazy_request;
}
#endif /* _INTEL_RINGBUFFER_H_ */