linux-kernel - Re: [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO

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: <20111222234135.GB7056@barrios-laptop.redhat.com>
Date:	Fri, 23 Dec 2011 08:41:35 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Stefan Hajnoczi <stefanha@...il.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Chris Wright <chrisw@...s-sol.org>,
	Jens Axboe <axboe@...nel.dk>,
	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Christoph Hellwig <hch@...radead.org>,
	Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 0/6][RFC] virtio-blk: Change I/O path from request to BIO

On Thu, Dec 22, 2011 at 12:57:40PM +0000, Stefan Hajnoczi wrote:
> On Wed, Dec 21, 2011 at 1:00 AM, Minchan Kim <minchan@...nel.org> wrote:
> > This patch is follow-up of Christohp Hellwig's work
> > [RFC: ->make_request support for virtio-blk].
> > http://thread.gmane.org/gmane.linux.kernel/1199763
> >
> > Quote from hch
> > "This patchset allows the virtio-blk driver to support much higher IOP
> > rates which can be driven out of modern PCI-e flash devices.  At this
> > point it really is just a RFC due to various issues."
> 
> Basic question to make sure I understood this series: does this patch
> bypass the guest I/O scheduler (but then you added custom batching
> code into virtio_blk.c)?

Right.

> 
> If you're stumped by the performance perhaps compare blktraces of the
> request approach vs the bio approach.  We're probably performing I/O
> more CPU-efficiently but the I/O pattern itself is worse.

You mean I/O scheduler have many techniques to do well in I/O pattern?
That's what I want to discuss in this RFC.

I guess request layer have many techniques proved during long time
to do well I/O but BIO-based drvier ignores them for just reducing locking
overhead. Of course, we can add such techniques to BIO-batch driver like 
custom-batch in this series. But it needs lots of work, is really duplication,
and will have a problem on maintenance.

I would like to listen opinions whether this direction is good or bad.

> 
> Stefan

-- 
Kind regards,
Minchan Kim
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/