Hi, On Wednesday, October 04, 2017 07:23:07 PM Hunter, Adrian wrote: > > -----Original Message----- > > From: Bartlomiej Zolnierkiewicz [mailto:b.zolnierkie@xxxxxxxxxxx] > > Sent: Wednesday, October 4, 2017 12:40 PM > > To: Linus Walleij <linus.walleij@xxxxxxxxxx> > > Cc: Hunter, Adrian <adrian.hunter@xxxxxxxxx>; Ulf Hansson > > <ulf.hansson@xxxxxxxxxx>; linux-mmc <linux-mmc@xxxxxxxxxxxxxxx>; linux- > > block <linux-block@xxxxxxxxxxxxxxx>; linux-kernel <linux- > > kernel@xxxxxxxxxxxxxxx>; Bough Chen <haibo.chen@xxxxxxx>; Alex > > Lemberg <alex.lemberg@xxxxxxxxxxx>; Nowak, Mateusz > > <mateusz.nowak@xxxxxxxxx>; Yuliy Izrailov <Yuliy.Izrailov@xxxxxxxxxxx>; > > Jaehoon Chung <jh80.chung@xxxxxxxxxxx>; Dong Aisheng > > <dongas86@xxxxxxxxx>; Das Asutosh <asutoshd@xxxxxxxxxxxxxx>; > > Zhangfei Gao <zhangfei.gao@xxxxxxxxx>; Sahitya Tummala > > <stummala@xxxxxxxxxxxxxx>; Harjani Ritesh <riteshh@xxxxxxxxxxxxxx>; > > Venu Byravarasu <vbyravarasu@xxxxxxxxxx>; Shawn Lin <shawn.lin@rock- > > chips.com>; Christoph Hellwig <hch@xxxxxx> > > Subject: Re: [PATCH V9 13/15] mmc: block: Add CQE and blk-mq support > > > > > > Hi, > > > > On Wednesday, October 04, 2017 09:39:45 AM Linus Walleij wrote: > > > On Fri, Sep 22, 2017 at 2:37 PM, Adrian Hunter <adrian.hunter@xxxxxxxxx> > > wrote: > > > > > > > Add CQE support to the block driver, including: > > > > - optionally using DCMD for flush requests > > > > - "manually" issuing discard requests > > > > - issuing read / write requests to the CQE > > > > - supporting block-layer timeouts > > > > - handling recovery > > > > - supporting re-tuning > > > > > > > > CQE offers 25% - 50% better random multi-threaded I/O. There is a > > > > slight (e.g. 2%) drop in sequential read speed but no observable > > > > change to sequential write. > > > > > > > > CQE automatically sends the commands to complete requests. However > > > > it only supports reads / writes and so-called "direct commands" > > > > (DCMD). Furthermore DCMD is limited to one command at a time, but > > discards require 3 commands. > > > > That makes issuing discards through CQE very awkward, but some CQE's > > > > don't support DCMD anyway. So for discards, the existing non-CQE > > > > approach is taken, where the mmc core code issues the 3 commands one > > at a time i.e. > > > > mmc_erase(). Where DCMD is used, is for issuing flushes. > > > > > > > > For host controllers without CQE support, blk-mq support is extended > > > > to synchronous reads/writes or, if the host supports > > > > CAP_WAIT_WHILE_BUSY, asynchonous reads/writes. The advantage of > > > > asynchronous reads/writes is that it allows the preparation of the > > > > next request while the current request is in progress. > > > > > > > > Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx> > > > > > > I am trying to wrap my head around this large patch. The size makes it > > > hard but I am doing my best. > > > > I also think that this patch should be split on two patches. The 1st one > > introducing blk-mq and the 2nd one adding CQE support. > > > > [ I don't agree that they make more sense together, on the contrary, > > it is very difficult to properly analyze blk-mq changes on their > > own while there are mixed with CQE related ones. ] > > The CQE and non-CQE code paths are clearly marked. But maybe you The combined patch is > 1 kLOC which is a lot and since the CQE and non-CQE code paths are clearly marked it should be really easy to split them. > are asking what the code would look like if we *never* had to support CQE. > And my point is we *do* have to support CQE. We *do* but not in the same step, it is just normal kernel engineering practice to split patches on logical changes. This is not asking about something extraordinary. > Do you have any questions about the code? I would really hope to see more documentation about blk-mq changes first before starting to review it. The patch description documents CQE changes but not blk-mq ones and the code itself is also lacking in-code documentation describing new functions added for blk-mq. Best regards, -- Bartlomiej Zolnierkiewicz Samsung R&D Institute Poland Samsung Electronics -- To unsubscribe from this list: send the line "unsubscribe linux-mmc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
