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From: Paolo Bonzini <pbonzini@redhat.com>
To: "Emilio G. Cota" <cota@braap.org>, Pranith Kumar <bobby.prani@gmail.com>
Cc: "Richard Henderson" <rth@twiddle.net>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"open list:All patches CC here" <qemu-devel@nongnu.org>,
	"Markus Armbruster" <armbru@redhat.com>
Subject: Re: [Qemu-devel] [RFC PATCH] qht: Align sequence lock to cache line
Date: Tue, 25 Oct 2016 22:58:00 +0200	[thread overview]
Message-ID: <7012eb7a-929a-519b-cf0d-48c62d594589@redhat.com> (raw)
In-Reply-To: <20161025204515.GA22860@flamenco>



On 25/10/2016 22:45, Emilio G. Cota wrote:
> On Tue, Oct 25, 2016 at 16:35:48 -0400, Pranith Kumar wrote:
>> On Tue, Oct 25, 2016 at 4:02 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>
>>>
>>>> I've written a patch (see below) to take the per-bucket sequence locks.
>>>
>>> What's the performance like?
>>>
>>
>> Applying only this patch, the perf numbers are similar to the 128
>> cache line alignment you suggested.
> 
> That makes sense. Having a single seqlock per bucket is simple and fast;
> note that bucket chains should be very short (we use good hashing and
> automatic resize for this purpose).

But why do we get such worse performance in the 100% reader case?  (And
even more puzzling, why does Pranith's original patch improve
performance instead of causing more cache misses?)

Thanks,

Paolo

  reply	other threads:[~2016-10-25 20:58 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-10-25 15:35 [Qemu-devel] [RFC PATCH] qht: Align sequence lock to cache line Pranith Kumar
2016-10-25 15:41 ` Paolo Bonzini
2016-10-25 15:49   ` Pranith Kumar
2016-10-25 15:54     ` Paolo Bonzini
2016-10-25 19:12       ` Pranith Kumar
2016-10-25 20:02         ` Paolo Bonzini
2016-10-25 20:35           ` Pranith Kumar
2016-10-25 20:45             ` Emilio G. Cota
2016-10-25 20:58               ` Paolo Bonzini [this message]
2016-10-25 20:55 ` Emilio G. Cota

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