From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>, linux-kernel@vger.kernel.org
Cc: brouer@redhat.com
Subject: Re: [PATCH 1/3] ptr_ring: batch ring zeroing
Date: Fri, 14 Apr 2017 15:52:23 +0800 [thread overview]
Message-ID: <97915bd0-ef22-4e67-1b18-3522e2369fda@redhat.com> (raw)
In-Reply-To: <19f56d99-279a-5a8b-39a7-1017a3cb4bdd@redhat.com>
On 2017年04月12日 16:03, Jason Wang wrote:
>
>
> On 2017年04月07日 13:49, Michael S. Tsirkin wrote:
>> A known weakness in ptr_ring design is that it does not handle well the
>> situation when ring is almost full: as entries are consumed they are
>> immediately used again by the producer, so consumer and producer are
>> writing to a shared cache line.
>>
>> To fix this, add batching to consume calls: as entries are
>> consumed do not write NULL into the ring until we get
>> a multiple (in current implementation 2x) of cache lines
>> away from the producer. At that point, write them all out.
>>
>> We do the write out in the reverse order to keep
>> producer from sharing cache with consumer for as long
>> as possible.
>>
>> Writeout also triggers when ring wraps around - there's
>> no special reason to do this but it helps keep the code
>> a bit simpler.
>>
>> What should we do if getting away from producer by 2 cache lines
>> would mean we are keeping the ring moe than half empty?
>> Maybe we should reduce the batching in this case,
>> current patch simply reduces the batching.
>>
>> Notes:
>> - it is no longer true that a call to consume guarantees
>> that the following call to produce will succeed.
>> No users seem to assume that.
>> - batching can also in theory reduce the signalling rate:
>> users that would previously send interrups to the producer
>> to wake it up after consuming each entry would now only
>> need to do this once in a batch.
>> Doing this would be easy by returning a flag to the caller.
>> No users seem to do signalling on consume yet so this was not
>> implemented yet.
>>
>> Signed-off-by: Michael S. Tsirkin<mst@redhat.com>
>> ---
>>
>> Jason, I am curious whether the following gives you some of
>> the performance boost that you see with vhost batching
>> patches. Is vhost batching on top still helpful?
>
> The patch looks good to me, will have a test for vhost batching patches.
>
> Thanks
Still helpful:
before this patch: 1.84Mpps
with this patch: 2.00Mpps
with batch dequeuing: 2.30Mpps
Acked-by: Jason Wang <jasowang@redhat.com>
Thanks
next prev parent reply other threads:[~2017-04-14 7:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-07 5:49 [PATCH 1/3] ptr_ring: batch ring zeroing Michael S. Tsirkin
2017-04-07 5:50 ` [PATCH 2/3] ringtest: support test specific parameters Michael S. Tsirkin
2017-04-07 5:50 ` [PATCH 3/3] ptr_ring: support testing different batching sizes Michael S. Tsirkin
2017-04-08 12:14 ` [PATCH 1/3] ptr_ring: batch ring zeroing Jesper Dangaard Brouer
2017-05-09 13:33 ` Michael S. Tsirkin
2017-05-10 3:30 ` Jason Wang
2017-05-10 12:22 ` Michael S. Tsirkin
2017-05-10 9:18 ` Jesper Dangaard Brouer
2017-05-10 12:20 ` Michael S. Tsirkin
2017-04-12 8:03 ` Jason Wang
2017-04-14 7:52 ` Jason Wang [this message]
2017-04-14 21:00 ` Michael S. Tsirkin
2017-04-18 2:16 ` Jason Wang
2017-04-14 22:50 ` Michael S. Tsirkin
2017-04-18 2:18 ` Jason Wang
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=97915bd0-ef22-4e67-1b18-3522e2369fda@redhat.com \
--to=jasowang@redhat.com \
--cc=brouer@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mst@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).