From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51946) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7JtB-00063T-Uv for qemu-devel@nongnu.org; Mon, 30 May 2016 05:53:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1b7Jt1-0006Fj-UO for qemu-devel@nongnu.org; Mon, 30 May 2016 05:53:36 -0400 Received: from mx-v6.kamp.de ([2a02:248:0:51::16]:42598 helo=mx01.kamp.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1b7Jt1-0006E7-KO for qemu-devel@nongnu.org; Mon, 30 May 2016 05:53:27 -0400 References: <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> <574C0822.6040004@kamp.de> <20160530094719.GC4436@noname.str.redhat.com> From: Peter Lieven Message-ID: <574C0D92.5090302@kamp.de> Date: Mon, 30 May 2016 11:53:22 +0200 MIME-Version: 1.0 In-Reply-To: <20160530094719.GC4436@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 11:47 schrieb Kevin Wolf: > Am 30.05.2016 um 11:30 hat Peter Lieven geschrieben: >> 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. > The problem with "we'll rework the tests later" is always that it > doesn't happen if the patches for the functional parts and a workaround > for the test case are merged. > > I don't think that making 077 cover both cases should be hard or take > much time, it just needs to be done. If all the time for writing emails > in this thread had been used to work on the test case, it would already > be done. Understood. If you can give a hint how to get the value of the align parameter into the test script I can try. Otherwise the test will fail also if any block driver has an align value that is not equal to 512. Peter