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List: linux-api
Subject: Re: [resend][PATCH] Added PR_SET_PROCTITLE_AREA option for prctl()
From: KOSAKI Motohiro <kosaki.motohiro () jp ! fujitsu ! com>
Date: 2009-10-13 0:03:22
Message-ID: 20091013083744.C747.A69D9226 () jp ! fujitsu ! com
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> On Tue, 13 Oct 2009 04:03:45 +0900 (JST)
> KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
>
> > > Start simple. What's wrong with mutex_lock() on the reader and writer
> > > sides? rwsems might be OK too.
> > >
> > > In both cases we should think about whether persistent readers can
> > > block the writer excessively though.
> >
> > I thought your mention seems reasonable. then I mesured various locking
> > performance.
> >
> > no-contention read-read contetion read-write contention
> > w/o patch 4627 ms 7575 ms N/A
> > mutex 5717 ms 33872 ms (!) 14793 ms
> > rw-semaphoe 6846 ms 10734 ms 36156 ms (!)
> > seqlock 4754 ms 7558 ms 9373 ms
> >
> > Umm, seqlock is significantly better than other.
>
> Sure, but even the worst case there is 1,000,000 operations in 34
> seconds (yes?). 33 microseconds for a /proc read while under a specific
> local DoS attack is OK!
>
> If so then all implementations are acceptable and we should choose the
> simplest, most-obviously-correct one.
Hm, ok!
I had guessed you don't accept this slowness. but my guess was wrong.
I have no objection to use rw-semaphoe if you accept it.
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