Nicholas Piggin 68b2fc714f tty: hvc: hvc_poll() fix read loop batching ... Commit ec97eaad13 ("tty: hvc: hvc_poll() break hv read loop") removes get_chars batching entirely, which slows down large console operations like paste -- virtio console "feels worse than a 9600 baud serial line," reports Matteo. This adds back batching in a more latency friendly way. If the caller can sleep then we try to fill the entire flip buffer, releasing the lock and scheduling between each iteration. If it can not sleep, then batches are limited to 128 bytes. Matteo confirms this fixes the performance problem. Latency testing the powerpc OPAL console with OpenBMC UART with a large paste shows about 0.25ms latency, which seems reasonable. 10ms latencies were typical for this case before the latency breaking work, so we still see most of the benefit. kopald-1204 0d.h. 5us : hvc_poll <-hvc_handle_interrupt kopald-1204 0d.h. 5us : __hvc_poll <-hvc_handle_interrupt kopald-1204 0d.h. 5us : _raw_spin_lock_irqsave <-__hvc_poll kopald-1204 0d.h. 5us : tty_port_tty_get <-__hvc_poll kopald-1204 0d.h. 6us : _raw_spin_lock_irqsave <-tty_port_tty_get kopald-1204 0d.h. 6us : _raw_spin_unlock_irqrestore <-tty_port_tty_get kopald-1204 0d.h. 6us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 7us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 7us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 36us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 36us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 36us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 65us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 65us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 66us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 94us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 95us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 95us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 124us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 124us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 125us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 154us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 154us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 154us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 183us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 184us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 184us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 213us : tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 213us : __tty_buffer_request_room <-__hvc_poll kopald-1204 0d.h. 213us+: opal_get_chars <-__hvc_poll kopald-1204 0d.h. 242us : _raw_spin_unlock_irqrestore <-__hvc_poll kopald-1204 0d.h. 242us : tty_flip_buffer_push <-__hvc_poll kopald-1204 0d.h. 243us : queue_work_on <-tty_flip_buffer_push kopald-1204 0d.h. 243us : tty_kref_put <-__hvc_poll kopald-1204 0d.h. 243us : hvc_kick <-hvc_handle_interrupt kopald-1204 0d.h. 243us : wake_up_process <-hvc_kick kopald-1204 0d.h. 244us : try_to_wake_up <-hvc_kick kopald-1204 0d.h. 244us : _raw_spin_lock_irqsave <-try_to_wake_up kopald-1204 0d.h. 244us : _raw_spin_unlock_irqrestore <-try_to_wake_up Reported-by: Matteo Croce <mcroce@redhat.com> Tested-by: Matteo Croce <mcroce@redhat.com> Tested-by: Jason Gunthorpe <jgg@mellanox.com> Tested-by: Leon Romanovsky <leonro@mellanox.com> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>		2018-09-10 18:04:31 +02:00
..
hvc_console.c	tty: hvc: hvc_poll() fix read loop batching	2018-09-10 18:04:31 +02:00
hvc_console.h	tty: hvc: introduce the hv_ops.flush operation for hvc drivers	2018-07-23 20:13:20 +10:00
hvc_dcc.c	tty: hvc: Remove redundant license text	2017-11-08 13:08:12 +01:00
hvc_irq.c	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
hvc_iucv.c	treewide: kzalloc() -> kcalloc()	2018-06-12 16:19:22 -07:00
hvc_opal.c	powerpc/powernv: provide a console flush operation for opal hvc driver	2018-08-20 20:19:54 +10:00
hvc_riscv_sbi.c	tty: New RISC-V SBI console driver	2018-03-09 10:19:28 -08:00
hvc_rtas.c	tty: hvc: Remove redundant license text	2017-11-08 13:08:12 +01:00
hvc_udbg.c	tty: hvc: Remove redundant license text	2017-11-08 13:08:12 +01:00
hvc_vio.c	tty: hvc: Remove redundant license text	2017-11-08 13:08:12 +01:00
hvc_xen.c	tty: hvc: Remove redundant license text	2017-11-08 13:08:12 +01:00
hvcs.c	treewide: kmalloc() -> kmalloc_array()	2018-06-12 16:19:22 -07:00
hvsi.c	tty: hvc: Remove redundant license text	2017-11-08 13:08:12 +01:00
hvsi_lib.c	License cleanup: add SPDX GPL-2.0 license identifier to files with no license	2017-11-02 11:10:55 +01:00
Kconfig	TTY/Serial driver patches for 4.17-rc1	2018-04-04 18:43:49 -07:00
Makefile	TTY/Serial driver patches for 4.17-rc1	2018-04-04 18:43:49 -07:00