From: Jason Wang <jasowang@redhat.com>
To: "Michael S. Tsirkin" <mst@redhat.com>
Cc: linux-kernel@vger.kernel.org, brouer@redhat.com
Subject: Re: [PATCH 1/3] ptr_ring: batch ring zeroing
Date: Tue, 18 Apr 2017 10:18:59 +0800 [thread overview]
Message-ID: <57d767c5-86cc-0ba4-182f-aea6d4750670@redhat.com> (raw)
In-Reply-To: <20170415014859-mutt-send-email-mst@kernel.org>
On 2017年04月15日 06:50, Michael S. Tsirkin wrote:
> On Fri, Apr 14, 2017 at 03:52:23PM +0800, Jason Wang wrote:
>>
>> 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
> Just a thought: could you test dropping the consumer spinlock
> completely? Just around the peek?
2% improvement for dropping spinlock around peeking, 2% more for
dropping spinlock for consuming.
>
> As I said previously, perf c2c tool should be helpful
> to locate sources latency related to cache.
>
perf c2c indeeds shows some false sharing were reduced by this patch.
But it does not show obvious different with batch dequeuing on top.
Thanks
>> Acked-by: Jason Wang <jasowang@redhat.com>
>>
>> Thanks
prev parent reply other threads:[~2017-04-18 2:19 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
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 [this message]
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=57d767c5-86cc-0ba4-182f-aea6d4750670@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).