From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48010) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7JWn-0000Jp-RW for qemu-devel@nongnu.org; Mon, 30 May 2016 05:30:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b7JWZ-00028a-Iu for qemu-devel@nongnu.org; Mon, 30 May 2016 05:30:29 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:49663 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7JWZ-00028P-9N for qemu-devel@nongnu.org; Mon, 30 May 2016 05:30:15 -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> <574BDCC4.8000704@kamp.de> <20160530082412.GB4436@noname.str.redhat.com> From: Peter Lieven Message-ID: <574C0822.6040004@kamp.de> Date: Mon, 30 May 2016 11:30:10 +0200 MIME-Version: 1.0 In-Reply-To: <20160530082412.GB4436@noname.str.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 Cc: Fam Zheng , Paolo Bonzini , qemu-block@nongnu.org, qemu-devel@nongnu.org, stefanha@redhat.com, mreitz@redhat.com Am 30.05.2016 um 10:24 schrieb Kevin Wolf: > Am 30.05.2016 um 08:25 hat Peter Lieven geschrieben: >> 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. > Yes, but my point is that we may need to rework 077 anyway if we don't > only want to make it pass again, but to cover all relevant paths, too. > We got a new code path and it's unlikely that the existing tests covered > both the old code path and the new one. So you would postpone this patch until 077 is reworked? I found this one a nice improvement and 077 might take some time. Peter