Re: [RFC][PATCH] Reduce ext3 allocate-with-reservation lock latencies

[Mingming Cao <cmm@us.ibm.com>]

On Thu, 2005-04-28 at 12:12 -0400, Lee Revell wrote:
> On Thu, 2005-04-28 at 00:37 -0700, Mingming Cao wrote:
> > On Wed, 2005-04-27 at 23:45 -0400, Lee Revell wrote:
> > > On Fri, 2005-04-22 at 15:10 -0700, Mingming Cao wrote:
> > > > Please review. I have tested on fsx on SMP box. Lee, if you got time,
> > > > please try this patch.
> > > 
> > > I have tested and this does fix the problem.  I ran my tests and no ext3
> > > code paths showed up on the latency tracer at all, it never went above
> > > 33 usecs.
> > > 
> > Thanks, Lee.
> > 
> > The patch survived on many fsx test over 20 hours on a 2cpu machine.
> > Tested the patch on the same machine with tiobench (1-64 threads), and
> > untar a kernel tree test, no regression there.
> > However I see about 5-7% throughput drop on dbench with 16 threads. It
> > probably due to the cpu cost that we have discussed.
> 
> Hmm, I guess someone needs to test it on a bigger system.  AFAICT this
> should improve SMP scalability quite a bit.  Maybe that lock is rarely
> contended.

Probably. I will try it on a relatively full filesystem(where bitmap
scan to find a free block takes time), and on a 4 cpu box with many
threads allocating at the same time.

Mingming

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