> -----Original Message----- > From: Bartlomiej Zolnierkiewicz [mailto:[email protected]] > Sent: Wednesday, October 4, 2017 12:40 PM > To: Linus Walleij <[email protected]> > Cc: Hunter, Adrian <[email protected]>; Ulf Hansson > <[email protected]>; linux-mmc <[email protected]>; linux- > block <[email protected]>; linux-kernel <linux- > [email protected]>; Bough Chen <[email protected]>; Alex > Lemberg <[email protected]>; Nowak, Mateusz > <[email protected]>; Yuliy Izrailov <[email protected]>; > Jaehoon Chung <[email protected]>; Dong Aisheng > <[email protected]>; Das Asutosh <[email protected]>; > Zhangfei Gao <[email protected]>; Sahitya Tummala > <[email protected]>; Harjani Ritesh <[email protected]>; > Venu Byravarasu <[email protected]>; Shawn Lin <shawn.lin@rock- > chips.com>; Christoph Hellwig <[email protected]> > 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 <[email protected]> > 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 <[email protected]> > > > > 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 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. Do you have any questions about the code?
