Re: Lockless page cache test results

[Nick Piggin]

Jens Axboe wrote:
> Hi,
>
> Running a splice benchmark on a 4-way IPF box, I decided to give the
> lockless page cache patches from Nick a spin. I've attached the results
> as a png, it pretty much speaks for itself.
>
> The test in question splices a 1GiB file to a pipe and then splices that
> to some output. Normally that output would be something interesting, in
> this case it's simply /dev/null. So it tests the input side of things
> only, which is what I wanted to do here. To get adequate runtime, the
> operation is repeated a number of times (120 in this example). The
> benchmark does that number of loops with 1, 2, 3, and 4 clients each
> pinned to a private CPU. The pinning is mainly done for more stable
> results.

Thanks Jens!

It's interesting, single threaded performance is down a little. Is
this significant? In some other results you showed me with 3 splices
each running on their own file (ie. no tree_lock contention), lockless
looked slightly faster on the same machine.

In my microbenchmarks, single threaded lockless is quite a bit faster
than vanilla on both P4 and G5.

It could well be that the speculative get_page operation is naturally
a bit slower on Itanium CPUs -- there is a different mix of barriers,
reads, writes, etc. If only someone gave me an IPF system... ;)

As you said, it would be nice to see how this goes when the other end
are 4 gigabit pipes or so... And then things like specweb and file
serving workloads.

Nick

--
SUSE Labs, Novell Inc.

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