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From: Dipankar Sarma <dipankar@in.ibm.com>
To: "David S. Miller" <davem@redhat.com>
Cc: wli@holomorphy.com, akpm@digeo.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: 2.5.69-mm1
Date: Tue, 6 May 2003 21:17:55 +0530	[thread overview]
Message-ID: <20030506154755.GD9875@in.ibm.com> (raw)
In-Reply-To: <20030506.072051.45141886.davem@redhat.com>

On Tue, May 06, 2003 at 07:20:51AM -0700, David S. Miller wrote:
>    From: Dipankar Sarma <dipankar@in.ibm.com>
>    
>    Provided there isn't a very heavy contention among readers for the
>    spin_lock.
> 
> Even if there are thousands of readers trying to get the lock
> at the same time, unless your hold time is significant these
> readers will merely thrash the cache getting the rwlock_t.
> And then thrash it again to release the rwlock_t.

And now ISTR that this is indeed the case, atleast going by
what we saw with "chat" microbenchmarks (fwiw :)).
Hold times weren't very high and most of the performance penalty
came from bouncing of the rwlock cacheline, which prompted us to
write a RCU-based patch for lockfree lookup from fd table.

Thanks
Dipankar

WARNING: multiple messages have this Message-ID (diff)
From: Dipankar Sarma <dipankar@in.ibm.com>
To: "David S. Miller" <davem@redhat.com>
Cc: wli@holomorphy.com, akpm@digeo.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: 2.5.69-mm1
Date: Tue, 6 May 2003 21:17:55 +0530	[thread overview]
Message-ID: <20030506154755.GD9875@in.ibm.com> (raw)
In-Reply-To: <20030506.072051.45141886.davem@redhat.com>

On Tue, May 06, 2003 at 07:20:51AM -0700, David S. Miller wrote:
>    From: Dipankar Sarma <dipankar@in.ibm.com>
>    
>    Provided there isn't a very heavy contention among readers for the
>    spin_lock.
> 
> Even if there are thousands of readers trying to get the lock
> at the same time, unless your hold time is significant these
> readers will merely thrash the cache getting the rwlock_t.
> And then thrash it again to release the rwlock_t.

And now ISTR that this is indeed the case, atleast going by
what we saw with "chat" microbenchmarks (fwiw :)).
Hold times weren't very high and most of the performance penalty
came from bouncing of the rwlock cacheline, which prompted us to
write a RCU-based patch for lockfree lookup from fd table.

Thanks
Dipankar
--
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  reply	other threads:[~2003-05-06 15:33 UTC|newest]

Thread overview: 28+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2003-05-05  6:16 2.5.69-mm1 Andrew Morton
2003-05-05  6:16 ` 2.5.69-mm1 Andrew Morton
2003-05-05 15:32 ` 2.5.69-mm1 Andrei Ivanov
2003-05-05 16:45   ` 2.5.69-mm1 Greg KH
2003-05-06  9:49     ` 2.5.69-mm1 Andrei Ivanov
2003-05-05 18:44   ` 2.5.69-mm1 Andrew Morton
2003-05-05 21:01 ` 2.5.69-mm1 William Lee Irwin III
2003-05-05 21:01   ` 2.5.69-mm1 William Lee Irwin III
2003-05-06 11:09   ` 2.5.69-mm1 Dipankar Sarma
2003-05-06 11:09     ` 2.5.69-mm1 Dipankar Sarma
2003-05-06 12:02     ` 2.5.69-mm1 David S. Miller
2003-05-06 12:02       ` 2.5.69-mm1 David S. Miller
2003-05-06 15:25       ` 2.5.69-mm1 Dipankar Sarma
2003-05-06 15:25         ` 2.5.69-mm1 Dipankar Sarma
2003-05-06 14:20         ` 2.5.69-mm1 David S. Miller
2003-05-06 14:20           ` 2.5.69-mm1 David S. Miller
2003-05-06 15:47           ` Dipankar Sarma [this message]
2003-05-06 15:47             ` 2.5.69-mm1 Dipankar Sarma
2003-05-05 21:02 ` 2.5.69-mm1 William Lee Irwin III
2003-05-05 21:02   ` 2.5.69-mm1 William Lee Irwin III
2003-05-06 14:33 ` 2.5.69-mm1 Steven Cole
2003-05-06 14:33   ` 2.5.69-mm1 Steven Cole
2003-05-06 15:33   ` 2.5.69-mm1 Andrew Morton
2003-05-06 15:33     ` 2.5.69-mm1 Andrew Morton
2003-05-06 15:36     ` 2.5.69-mm1 Eric W. Biederman
2003-05-06 15:36       ` 2.5.69-mm1 Eric W. Biederman
2003-05-06 16:35       ` 2.5.69-mm1 Steven Cole
2003-05-06 16:35         ` 2.5.69-mm1 Steven Cole

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