[ovs-dev] [PATCH] coverage: Add coverage_try_clear() for performance-critical threads.

[Traynor, Kevin]

> -----Original Message-----
> From: dev [mailto:dev-bounces at openvswitch.org] On Behalf Of Daniele Di
> Proietto
> Sent: Monday, August 24, 2015 7:08 PM
> To: Alex Wang
> Cc: dev; Ilya Maximets
> Subject: Re: [ovs-dev] [PATCH] coverage: Add coverage_try_clear() for
> performance-critical threads.
> 
> Hi Alex,
> 
> sorry for the delay and thanks for taking care of this.
> I couldn't experience any noticeable performance drop.

Same for me - no performance drop in my tests.

> 
> Acked-by: Daniele Di Proietto <diproiettod at vmware.com>
> 
> On 22/08/2015 16:44, "Alex Wang" <alexw at nicira.com> wrote:
> 
> >Sorry for the delay of pushing this and related dpdk patches,
> >
> >Want to spend some time next week measuring the performance impact,~
> >
> >Thanks,
> >Alex Wang,
> >
> >On Fri, Aug 21, 2015 at 12:48 PM, Ben Pfaff <blp at nicira.com> wrote:
> >
> >> On Thu, Aug 13, 2015 at 11:48:49AM -0700, Alex Wang wrote:
> >> > For performance-critical threads like pmd threads, we currently make
> >>them
> >> > never call coverage_clear() to avoid contention over the global mutex
> >> > 'coverage_mutex'.  So, even though pmd thread still keeps updating
> >>their
> >> > thread-local coverage count, the count is never attributed to the
> >>global
> >> > total.  But it is useful to have them available.
> >> >
> >> > This commit makes this happen by implementing a non-contending version
> >> > of the clear function, coverage_try_clear().  The function will use
> >> > the ovs_mutex_trylock() and return immediately if the mutex cannot
> >> > be acquired.  Since threads like pmd thread are always busy-looping,
> >> > the lock will eventually be acquired.
> >> >
> >> > Requested-by: Ilya Maximets <i.maximets at samsung.com>
> >> > Signed-off-by: Alex Wang <alexw at nicira.com>
> >>
> >> This seems like an improvement.  I can imagine better data structures
> >> but I don't know whether they're worthwhile.
> >>
> >> Acked-by: Ben Pfaff <blp at nicira.com>
> >>
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