Lock contention in AIO
Slawa Olhovchenkov
slw at zxy.spb.ru
Thu Apr 13 11:59:05 UTC 2017
On Wed, Apr 12, 2017 at 05:21:02PM -0700, Adrian Chadd wrote:
> It's the same pages, right?
Perhaps.
> Is it just the refcounting locking that's
> causing it?
Don't know.
> I think the biggest thing here is to figure out how to have pages have
> a lifecycle where the refcount can be inc/dec (obviously >1, ie not in
> a state where you can dec to 0) via atomics, without grabbing a lock.
> That'll make this particular use case muuuuch faster.
>
> (dfbsd does this.)
I can try you patch.
> -a
>
>
> On 21 March 2017 at 09:42, Slawa Olhovchenkov <slw at zxy.spb.ru> wrote:
> > I am see lock contetntion cuased by aio read (same file segment from
> > multiple process simultaneous):
> >
> > 07.74% [26756] lock_delay @ /boot/kernel/kernel
> > 92.21% [24671] __mtx_lock_sleep
> > 52.14% [12864] vm_page_enqueue
> > 100.0% [12864] vm_fault_hold
> > 87.71% [11283] vm_fault_quick_hold_pages
> > 100.0% [11283] vn_io_fault1
> > 100.0% [11283] vn_io_fault
> > 99.88% [11270] aio_process_rw
> > 100.0% [11270] aio_daemon
> > 100.0% [11270] fork_exit
> > 00.12% [13] dofileread
> > 100.0% [13] kern_readv
> >
> > Is this know problem?
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