linux-kernel - Re: [PATCH 1/4] block: add scalable completion tracking of requests

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <bd83d2b6-3e7f-18c0-45d6-7b9f6c015722@fb.com>
Date:   Thu, 3 Nov 2016 07:38:55 -0600
From:   Jens Axboe <axboe@...com>
To:     Ming Lei <tom.leiming@...il.com>
CC:     Jens Axboe <axboe@...nel.dk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH 1/4] block: add scalable completion tracking of requests

On 11/03/2016 05:17 AM, Ming Lei wrote:
>> diff --git a/block/blk-core.c b/block/blk-core.c
>> index 0bfaa54d3e9f..ca77c725b4e5 100644
>> --- a/block/blk-core.c
>> +++ b/block/blk-core.c
>> @@ -2462,6 +2462,8 @@ void blk_start_request(struct request *req)
>>  {
>>         blk_dequeue_request(req);
>>
>> +       blk_stat_set_issue_time(&req->issue_stat);
>> +
>>         /*
>>          * We are now handing the request to the hardware, initialize
>>          * resid_len to full count and add the timeout handler.
>> @@ -2529,6 +2531,8 @@ bool blk_update_request(struct request *req, int error, unsigned int nr_bytes)
>>
>>         trace_block_rq_complete(req->q, req, nr_bytes);
>>
>> +       blk_stat_add(&req->q->rq_stats[rq_data_dir(req)], req);
>
> blk_update_request() is often called lockless, so it isn't good to
> do it here.

It's not really a concern, not for the legacy path here nor the mq one
where it is per sw context. The collisions are rare enough that it'll
skew the latencies a bit for that short window, but then go away again.
I'd much rather take that, than adding locking for this part.

-- 
Jens Axboe