linux-kernel - Re: [PATCH 0/3] use rwlock in order to reduce ep_poll

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Date:   Mon, 17 Dec 2018 10:01:19 -0800
From:   Davidlohr Bueso <dbueso@...e.de>
To:     Roman Penyaev <rpenyaev@...e.de>
Cc:     Jason Baron <jbaron@...mai.com>, Al Viro <viro@...iv.linux.org.uk>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] use rwlock in order to reduce ep_poll_callback()
 contention

On 2018-12-17 03:49, Roman Penyaev wrote:
> On 2018-12-13 19:13, Davidlohr Bueso wrote:
> Yes, good idea.  But frankly I do not want to bloat epoll-wait.c with
> my multi-writers-single-reader test case, because soon epoll-wait.c
> will become unmaintainable with all possible loads and set of
> different options.
> 
> Can we have a single, small and separate source for each epoll load?
> Easy to fix, easy to maintain, debug/hack.

Yes completely agree; I was actually thinking along those lines.

> 
>> I ran these patches on the 'wait' workload which is a epoll_wait(2)
>> stresser. On a 40-core IvyBridge it shows good performance
>> improvements for increasing number of file descriptors each of the 40
>> threads deals with:
>> 
>> 64   fds: +20%
>> 512  fds: +30%
>> 1024 fds: +50%
>> 
>> (Yes these are pretty raw measurements ops/sec). Unlike your
>> benchmark, though, there is only single writer thread, and therefore
>> is less ideal to measure optimizations when IO becomes available.
>> Hence it would be nice to also have this.
> 
> That's weird. One writer thread does not content with anybody, only 
> with
> consumers, so should not be any big difference.

Yeah so the irq optimization patch, which is known to boost numbers on 
this microbench, plays an important factor. I just put them all together 
when testing.

Thanks,
Davidlohr