linux-kernel - Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

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Date:	Thu, 1 Mar 2007 15:10:22 +0300
From:	Evgeniy Polyakov <johnpol@....mipt.ru>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Pavel Machek <pavel@....cz>, Theodore Tso <tytso@....edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ulrich Drepper <drepper@...hat.com>,
	linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@....com.au>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Zach Brown <zach.brown@...cle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Suparna Bhattacharya <suparna@...ibm.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [patch 00/13] Syslets, "Threadlets", generic AIO support, v3

On Thu, Mar 01, 2007 at 12:47:35PM +0100, Ingo Molnar (mingo@...e.hu) wrote:
> 
> * Ingo Molnar <mingo@...e.hu> wrote:
> 
> > > I also changed client socket to nonblocking mode with the same result 
> > > in epoll server. If you will find it broken, please send me corrected 
> > > to test too.
> > 
> > this line in evserver_kevent.c looks a bit fishy:
> 
> this one in evserver_kevent.c looks problematic too:
> 
>         shutdown(s, SHUT_RDWR);
>         close(s);
> 
> as evserver_epoll.c only does:
> 
>         close(s);
> 
> again, there might be TCP control flow differences due to this. [ Or the 
> removal of this shutdown() call might be a small speedup for the kevent 
> case ;) ]

:)

> Also, the order of fd and socket close() is different in the two cases. 
> It shouldnt make any difference - but that too just makes the results 
> harder to trust. Would it be so hard to introduce a single 
> handle_web_request() function that is exactly the same in the two tests? 
> All the queueing details (which are of course different in the epoll and 
> the kevent case) should be in the client function, which calls 
> handle_web_request().

I've removed shutdown - things are the same.

Sometimes kevent performance drops to lower numbers and its graph of
times needed to handle events has high platoes (with and without
shutdown - it was always), like this:

Percentage of the requests served within a certain time (ms)
50%    128
66%    486
75%    505
80%    507
90%    732
95%   3087	// something is wrong at this point
98%   9058
99%   9072
100%  15562 (longest request)

it is possible that threre are some other bugs in the server though,
which prevent sockets from being quicly closed and thus its processing
time increases - I do not know for sure the root of that event.

I separated epoll and kevent servers, since originally kevent server 
included additional kevent features, but then new ones were added 
and I moved slowly to the similar to epoll case.

Current version of the server was a pre-test one for lighttpd patches,
so essentially it should be like epoll except minor details.

> 	Ingo

-- 
	Evgeniy Polyakov
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