posix host: the timer create one ephemeral thread per one ticket

[laijs]

it is waste.
you can observe the ephemeral threads created/exited for every ticket by using make gdb.

linux/tools/lkl/lib/posix-host.c

Line 266 in 311a4ee

.sigev_notify = SIGEV_THREAD,

[thehajime]

@laijs what do you mean by make gdb ?

one alternative is #250 to use green threads, others would be thread pool-like implementation.

[laijs]

it is not easy to observe this behavior, make gdb is the best way to observe it in the test.

one ephemeral thread per one ticket is too much, we need to change it to use several threads instead. example: only one dedicated timer thread.

[laijs]

one alternative is #250 to use green threads, others would be thread pool-like implementation.

it is unrelated, timer_create() will create pthreads. it is not controlled by lkl-kernel.

[thehajime]

(thanks, I wasn't aware of make gdb in tools/lkl/Makefile)

if I understood correctly, creating/deleting one pthread per one clockevent makes huge overhead of creating pthread, context switches, etc. I thought green threads instead of pthread (including rewriting timer library, #250) helps to address those situations.

a thread pool (also replacing timer API) does the same.

[liuyuan10]

I find this link can be helpful: http://stackoverflow.com/questions/32283171/signal-handler-in-a-separate-pthread-using-timer-create The extra cost is parallel with LKL so it may not improve latency & throughput that much. But it can save overall CPU cost of LKL.

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On Wed, Feb 15, 2017 at 4:30 PM, Hajime Tazaki ***@***.***> wrote: (thanks, I wasn't aware of make gdb in tools/lkl/Makefile) if I understood correctly, creating/deleting one pthread per one clockevent makes huge overhead of creating pthread, context switches, etc. I thought green threads instead of pthread (including rewriting timer library, #250 <#250>) helps to address those situations. a thread pool (also replacing timer API) does the same. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#330 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AEVfUurv-Au7c1olGjHGdI-D1CD7mDxyks5rc5i-gaJpZM4MBpeN> .

[laijs]

librt uses rt_sigtimedwait() internal to implement the timer, the posix-host subsystem can also use a dedicated thread to use rt_sigtimedwait() and trigger the irq.

[tavip]

I thought about the dedicated thread approach, but you can only implement it safely (i.e. make sure the signal is coming to the dedicated thread) only in Linux (see SIGEV_THREAD_ID in timer_create) which would make it non-posix.