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Subject: Re: [PATCH] 2.5: push BKL out of llseek
From: Robert Love <rml@tech9.net>
To: Dave Jones <davej@suse.de>
Cc: Andrew Morton <akpm@zip.com.au>, Linus Torvalds <torvalds@transmeta.com>,
        viro@math.psu.edu, linux-kernel@vger.kernel.org
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On Tue, 2002-01-29 at 21:21, Dave Jones wrote:

>  did you benchmark with anything other than dbench ?

No, and I really don't want to hear how dbench is a terrible benchmark. 
I didn't craft the patch around dbench and I think, here at least,
dbench is an OK benchmark.  I ran it numerous times over multiple client
loads.

I think its clear there won't be a negative impact, because:

- acquiring the inode semaphore isn't any heavier (in the acquire
  case) than the BKL

- the lock contention on each inode semaphore is relatively
  zero

- besides just scaling badly with the using a global lock against
  all inodes, we use the BKL which in such workloads is already
  highly contested.

That said, I did do some lock profiling and latency tests.  Contention
was near-zero, but I only did 2-way testing.  Under the preemptible
kernel, while running dbench, scheduling latency improved 8.9%.

	Robert Love

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