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Re: [Qemu-devel] [PATCH v4 13/14] tb hash: track translated blocks with

From: Emilio G. Cota
Subject: Re: [Qemu-devel] [PATCH v4 13/14] tb hash: track translated blocks with qht
Date: Thu, 5 May 2016 17:41:13 -0400
User-agent: Mutt/1.5.23 (2014-03-12)

On Wed, May 04, 2016 at 07:22:16 -1000, Richard Henderson wrote:
> On 05/04/2016 05:36 AM, Emilio G. Cota wrote:
> >BTW in the last couple of days I did some more work beyond v4:
> >
> >- Added a benchmark (not a correctness test) to measure parallel
> >  performance of QHT (recall that test/qht-test is sequential.)
> >
> >- Added support for concurrent insertions as long as they're not to the
> >  same bucket, thus getting rid of the "external lock" requirement.
> >  This is not really needed for MTTCG because all insertions are supposed
> >  to be serialized by tb_lock; however, the feature (1) has no negative
> >  performance impact (just adds an unlikely() branch after lock acquisition
> >  on insertions/removals) and (2) could be useful for future (parallel)
> >  users of qht.
> >
> >Should I send this work as follow-up patches to v4 to ease review, or
> >should I send a v5 with them merged in?
> Let's handle these as follow-on, since we've already got multiple R-b tags 
> for v4.

OK, will submit the modifications next week.

BTW Benchmarking with the new test is giving me some interesting

For instance, I'm measuring a 5% lookup latency reduction
(single-threaded throughput goes from 45.84 to 48.41 M lookups/s)
if I remove support in qht for MRU promotions.

This is tempting me to just kill the feature, since resizing
works very well.  And it would save ~90 lines of code. Is anyone
against this?



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