Re: New lockless pagecache

[Nick Piggin <nickpiggin@yahoo.com.au>]

Alok kataria wrote:
> Hi Nick,
>
> I have collected performance numbers for the lock less page cache
> patch on the AIM - IO test.
> The performance numbers are collected for 1-100 tasks 1-50 tasks and
> 90-100 tasks  both for with and without your patch. This was done on
> 2.6.13 kernel.
> There's definite improvement when the tasks are small i.e ~50-70. But
> when the tasks go beyond 80, we see a large performance dip.
> I again profiled the 90-100 runs with spinlock's inlined, but couldn't
> understand the reason behind the performance difference.
>
> Please find attached the performance numbers as well as the oprofile logs.

Hi Alok,

Thanks very much for doing these numbers. Performance is improved
significantly at smaller numbers of tasks, as you say.

Unfortunately I can't pinpoint the reason why performance drops at
larger numbers. I could assume that the last remaining place that
used read_lock_irq for the tree_lock (wait_on_page_writeback_range)
got hurt when switching to spinlocks, but that would seem vary
unlikely.

I'll have to look into it further.

Thanks,
Nick

--
SUSE Labs, Novell Inc.

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