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

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Date:   Sat, 28 Dec 2019 10:03:49 -0700
From:   Jens Axboe <axboe@...nel.dk>
To:     Pavel Begunkov <asml.silence@...il.com>, io-uring@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/2] io_uring: batch getting pcpu references

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()?

I think that's better than the empty, not quite sure what that means.
If you're fine with that, I can just make that edit when applying.
The rest looks fine to me now.

-- 
Jens Axboe