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If a per-cpu work item hogs the CPU, it can prevent other work items from starting through concurrency management. A per-cpu workqueue which intends to host such CPU-hogging work items can choose to not participate in concurrency management by setting %WQ_CPU_INTENSIVE; however, this can be error-prone and difficult to debug when missed. This patch adds an automatic CPU usage based detection. If a concurrency-managed work item consumes more CPU time than the threshold (10ms by default) continuously without intervening sleeps, wq_worker_tick() which is called from scheduler_tick() will detect the condition and automatically mark it CPU_INTENSIVE. The mechanism isn't foolproof: * Detection depends on tick hitting the work item. Getting preempted at the right timings may allow a violating work item to evade detection at least temporarily. * nohz_full CPUs may not be running ticks and thus can fail detection. * Even when detection is working, the 10ms detection delays can add up if many CPU-hogging work items are queued at the same time. However, in vast majority of cases, this should be able to detect violations reliably and provide reasonable protection with a small increase in code complexity. If some work items trigger this condition repeatedly, the bigger problem likely is the CPU being saturated with such per-cpu work items and the solution would be making them UNBOUND. The next patch will add a debug mechanism to help spot such cases. v4: Documentation for workqueue.cpu_intensive_thresh_us added to kernel-parameters.txt. v3: Switch to use wq_worker_tick() instead of hooking into preemptions as suggested by Peter. v2: Lai pointed out that wq_worker_stopping() also needs to be called from preemption and rtlock paths and an earlier patch was updated accordingly. This patch adds a comment describing the risk of infinte recursions and how they're avoided. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> |
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irq | ||
wrappers | ||
asm-annotations.rst | ||
assoc_array.rst | ||
boot-time-mm.rst | ||
cachetlb.rst | ||
circular-buffers.rst | ||
cpu_hotplug.rst | ||
debug-objects.rst | ||
debugging-via-ohci1394.rst | ||
dma-api-howto.rst | ||
dma-api.rst | ||
dma-attributes.rst | ||
dma-isa-lpc.rst | ||
entry.rst | ||
errseq.rst | ||
genalloc.rst | ||
generic-radix-tree.rst | ||
genericirq.rst | ||
gfp_mask-from-fs-io.rst | ||
idr.rst | ||
index.rst | ||
kernel-api.rst | ||
kobject.rst | ||
kref.rst | ||
librs.rst | ||
local_ops.rst | ||
maple_tree.rst | ||
memory-allocation.rst | ||
memory-hotplug.rst | ||
mm-api.rst | ||
netlink.rst | ||
packing.rst | ||
padata.rst | ||
pin_user_pages.rst | ||
printk-basics.rst | ||
printk-formats.rst | ||
printk-index.rst | ||
protection-keys.rst | ||
rbtree.rst | ||
refcount-vs-atomic.rst | ||
symbol-namespaces.rst | ||
this_cpu_ops.rst | ||
timekeeping.rst | ||
tracepoint.rst | ||
unaligned-memory-access.rst | ||
watch_queue.rst | ||
workqueue.rst | ||
xarray.rst |