Re: 2.5.36-mm1 dbench 512 profiles

From: Hanna Linder (
Date: Fri Sep 20 2002 - 13:51:13 EST

--On Friday, September 20, 2002 05:03:58 -0700 William Lee Irwin III <> wrote:

> On Fri, Sep 20, 2002 at 01:29:28PM +0530, Maneesh Soni wrote:
>>> For a 32-way system fastwalk will perform badly from dcache_lock
>>> point of view, basically due to increased lock hold time.
>>> dcache_rcu-12 should reduce dcache_lock contention and hold time. The
>>> patch uses RCU infrastructer patch and read_barrier_depends patch.
>>> The patches are available in Read-Copy-Update section on lse site at
> On Fri, Sep 20, 2002 at 01:06:28AM -0700, William Lee Irwin III wrote:
>> ISTR Hubertus mentioning this at OLS, and it sounded like a problem to
>> me. I'm doing some runs with this to see if it fixes the problem.

        I mentioned it at OLS too. It was the point of my talk. Next
        time I will request a non 10am time slot!

> take its place. Ugly. OTOH the qualitative difference is striking. The
> interactive responsiveness of the machine, even when entirely unloaded,
> is drastically improved, along with such nice things as init scripts
> and kernel compiles also markedly faster. I suspect this is just the
> wrong benchmark to show throughput benefits with.
> Also notable is that the system time was significantly reduced though
> I didn't log it. Essentially a long period of 100% system time is
> entered after a certain point in the benchmark, during which there are
> few (around 60 or 70) context switches in a second, and the duration
> of this period was shortened.

        Bill, you are saying that replacing dcache_rcu significantly
        improved system response time among other things?

        Perhaps it is time to reconsider replacing fastwalk with dcache_rcu.

        Viro? What are your objections?



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