From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35785) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7Gdb-0007vA-SD for qemu-devel@nongnu.org; Mon, 30 May 2016 02:25:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b7GdV-00027N-Ob for qemu-devel@nongnu.org; Mon, 30 May 2016 02:25:18 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:47351 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7GdV-00026P-ET for qemu-devel@nongnu.org; Mon, 30 May 2016 02:25:13 -0400 References: <1464100220-21317-1-git-send-email-pl@kamp.de> <20160526065045.GA10734@ad.usersys.redhat.com> <20160526071024.GB10734@ad.usersys.redhat.com> <413c4af8-ba30-bfbf-9a84-d1d92ddac0e4@redhat.com> <20160526083016.GD31052@ad.usersys.redhat.com> <4b26422f-9320-31a6-9dca-534bf0ea6086@redhat.com> <20160527003602.GG31052@ad.usersys.redhat.com> <20160527085559.GC5467@noname.redhat.com> From: Peter Lieven Message-ID: <574BDCC4.8000704@kamp.de> Date: Mon, 30 May 2016 08:25:08 +0200 MIME-Version: 1.0 In-Reply-To: <20160527085559.GC5467@noname.redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH V2] block/io: optimize bdrv_co_pwritev for small requests List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Kevin Wolf , Fam Zheng Cc: Paolo Bonzini , qemu-block@nongnu.org, qemu-devel@nongnu.org, stefanha@redhat.com, mreitz@redhat.com Am 27.05.2016 um 10:55 schrieb Kevin Wolf: > Am 27.05.2016 um 02:36 hat Fam Zheng geschrieben: >> On Thu, 05/26 11:20, Paolo Bonzini wrote: >>> On 26/05/2016 10:30, Fam Zheng wrote: >>>>>> This doesn't look too wrong... Should the right sequence of events be >>>>>> head/after_head or head/after_tail? It's probably simplest to just emit >>>>>> all four events. >>>> I've no idea. (That's why I leaned towards fixing the test case). >>> Well, fixing the testcase means knowing what events should be emitted. >>> >>> QEMU with Peter's patch emits head/after_head. If the right one is >>> head/after_tail, _both QEMU and the testcase_ need to be adjusted. Your >>> patch keeps the backwards-compatible route. >> Yes, I mean I was not very convinced in tweaking the events at all: each pair >> of them has been emitted around bdrv_aligned_preadv(), and the new branch >> doesn't do it anymore. So I don't see a reason to add events here. > Yes, if you can assume that anyone who uses the debug events know > exactly what the code looks like, adding the events here is pointless > because TAIL, AFTER_TAIL and for the greatest part also AFTER_HEAD are > essentially the same then. > > Having TAIL before the qiov change and AFTER_TAIL afterwards doesn't > make any difference, they could (and should) be called immediately one > after another if we wanted to keep the behaviour. > > I would agree that we should take a look at the test case and what it > actually wants to achieve before we can decide whether AFTER_HEAD and > TAIL/AFTER_TAIL would be the same (the former could trigger earlier if > there are two requests and only one is unaligned at the tail). Maybe we > even need to extend the test case now so that both paths (explicit read > of the tail and the shortcut) are covered. The part that actually blocks in 077 is # Sequential RMW requests on the same physical sector its expecting all 4 events around the RMW cycle. However, it seems that also other parts of 077 would need an adjustment and the output might differ depending on the alignment. So I guess we have to emit the events if we don't want to recode the whole 077 and make it aware of the alignment. Peter