linux-kernel - Re: submit bio directly from userspace

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Date:	Fri, 9 Oct 2015 08:32:51 -0600
From:	Jens Axboe <axboe@...nel.dk>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>,
	Mike Krinkin <krinkin.m.u@...il.com>,
	linux-kernel@...r.kernel.org
Cc:	hch@....de, kmo@...erainc.com
Subject: Re: submit bio directly from userspace

On 10/09/2015 05:41 AM, Dmitry Monakhov wrote:
> Mike Krinkin <krinkin.m.u@...il.com> writes:
>
>> Hi,
>>
>
>> i'm developing block layer workload simulator/player and need to
>> generate bios as close as possible to the ones in original workload.
>> To play workload i employ aio + O_DIRECT, but all IOs end up as bios
>> with SYNC flag set. So i wonder is there any way to control bios
>> flags from userspace or, maybe, any other options to generate
>> workload from userspace except aio + O_DIRECT with more precise
>> control over bio flags?
> 100% agree, I've investigated existing io-load replay tools and
> seems that they all use O_DIRECT(like btreplay) or
> buffered-aio/{sync_file_range,fadvise} ( like fio).
> So it looks like they all very inaccurate.
>
> Jens, what do to do to replay real load in order to test fs/ioscheduler
> harness? Are you interested in having such fine-tuning interface
> (probably guarded by CAP_SYS_ADMIN)?

A long time ago I wrote binject, which was meant to be a way to directly 
inject bio's on a queue:

http://git.kernel.dk/cgit/linux-block/log/?h=binject

It hasn't been moved forward, however. I haven't looked, is is SYNC the 
only flag addition we are worried about here? There are a slew of other 
flags that may impact how IO is treated. For instance, file system has 
tagged the request META. We can't pass that in either. Same is true for 
FLUSH or FUA writes.

-- 
Jens Axboe

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