linux-kernel - Re: [PATCH v4 2/2] io_uring: batch getting pcpu references

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Message-ID: <504de70b-f323-4ad1-6b40-4e73aa610643@gmail.com>
Date:   Sat, 28 Dec 2019 21:37:35 +0300
From:   Pavel Begunkov <asml.silence@...il.com>
To:     Jens Axboe <axboe@...nel.dk>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] io_uring: batch getting pcpu references

On 28/12/2019 20:03, Jens Axboe wrote:
> On 12/28/19 4:15 AM, Pavel Begunkov wrote:
>> On 28/12/2019 14:13, Pavel Begunkov wrote:
>>> percpu_ref_tryget() has its own overhead. Instead getting a reference
>>> for each request, grab a bunch once per io_submit_sqes().
>>>
>>> ~5% throughput boost for a "submit and wait 128 nops" benchmark.
>>>
>>> Signed-off-by: Pavel Begunkov <asml.silence@...il.com>
>>> ---
>>>  fs/io_uring.c | 26 +++++++++++++++++---------
>>>  1 file changed, 17 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>> index 7fc1158bf9a4..404946080e86 100644
>>> --- a/fs/io_uring.c
>>> +++ b/fs/io_uring.c
>>> @@ -1080,9 +1080,6 @@ static struct io_kiocb *io_get_req(struct io_ring_ctx *ctx,
>>>  	gfp_t gfp = GFP_KERNEL | __GFP_NOWARN;
>>>  	struct io_kiocb *req;
>>>  
>>> -	if (!percpu_ref_tryget(&ctx->refs))
>>> -		return NULL;
>>> -
>>>  	if (!state) {
>>>  		req = kmem_cache_alloc(req_cachep, gfp);
>>>  		if (unlikely(!req))
>>> @@ -1141,6 +1138,14 @@ static void io_free_req_many(struct io_ring_ctx *ctx, void **reqs, int *nr)
>>>  	}
>>>  }
>>>  
>>> +static void __io_req_free_empty(struct io_kiocb *req)
>>
>> If anybody have better naming (or a better approach at all), I'm all ears.
> 
> __io_req_do_free()?

Not quite clear what's the difference with __io_req_free() then

> 
> I think that's better than the empty, not quite sure what that means.

Probably, so. It was kind of "request without a bound sqe".
Does io_free_{hollow,empty}_req() sound better?

> If you're fine with that, I can just make that edit when applying.
> The rest looks fine to me now.
> 

Please do

-- 
Pavel Begunkov



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