Re: [PATCH v3 0/3] Add MMC software queue support

[Baolin Wang]

On Thu, 26 Sep 2019 at 20:08, Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:
>
> On 26/09/19 12:43 PM, Baolin Wang wrote:
> > Hi Adrian and Ulf,
> >
> > On Thu, 19 Sep 2019 at 13:59, Baolin Wang <baolin.wang@xxxxxxxxxx> wrote:
> >>
> >> Hi All,
> >>
> >> Now the MMC read/write stack will always wait for previous request is
> >> completed by mmc_blk_rw_wait(), before sending a new request to hardware,
> >> or queue a work to complete request, that will bring context switching
> >> overhead, especially for high I/O per second rates, to affect the IO
> >> performance.
> >>
> >> Thus this patch set will introduce the MMC software command queue support
> >> based on command queue engine's interfaces, and set the queue depth as 2,
> >> that means we do not need wait for previous request is completed and can
> >> queue 2 requests in flight. It is enough to let the irq handler always
> >> trigger the next request without a context switch and then ask the blk_mq
> >> layer for the next one to get queued, as well as avoiding a long latency.
> >>
> >> Moreover we can expand the MMC software queue interface to support
> >> MMC packed request or packed command instead of adding new interfaces,
> >> according to previosus discussion.
> >>
> >> Below are some comparison data with fio tool. The fio command I used
> >> is like below with changing the '--rw' parameter and enabling the direct
> >> IO flag to measure the actual hardware transfer speed in 4K block size.
> >>
> >> ./fio --filename=/dev/mmcblk0p30 --direct=1 --iodepth=20 --rw=read --bs=4K --size=512M --group_reporting --numjobs=20 --name=test_read
> >>
> >> My eMMC card working at HS400 Enhanced strobe mode:
> >> [    2.229856] mmc0: new HS400 Enhanced strobe MMC card at address 0001
> >> [    2.237566] mmcblk0: mmc0:0001 HBG4a2 29.1 GiB
> >> [    2.242621] mmcblk0boot0: mmc0:0001 HBG4a2 partition 1 4.00 MiB
> >> [    2.249110] mmcblk0boot1: mmc0:0001 HBG4a2 partition 2 4.00 MiB
> >> [    2.255307] mmcblk0rpmb: mmc0:0001 HBG4a2 partition 3 4.00 MiB, chardev (248:0)
> >>
> >> 1. Without MMC software queue
> >> I tested 3 times for each case and output a average speed.
> >>
> >> 1) Sequential read:
> >> Speed: 28.9MiB/s, 26.4MiB/s, 30.9MiB/s
> >> Average speed: 28.7MiB/s
> >>
> >> 2) Random read:
> >> Speed: 18.2MiB/s, 8.9MiB/s, 15.8MiB/s
> >> Average speed: 14.3MiB/s
> >>
> >> 3) Sequential write:
> >> Speed: 21.1MiB/s, 27.9MiB/s, 25MiB/s
> >> Average speed: 24.7MiB/s
> >>
> >> 4) Random write:
> >> Speed: 21.5MiB/s, 18.1MiB/s, 18.1MiB/s
> >> Average speed: 19.2MiB/s
> >>
> >> 2. With MMC software queue
> >> I tested 3 times for each case and output a average speed.
> >>
> >> 1) Sequential read:
> >> Speed: 44.1MiB/s, 42.3MiB/s, 44.4MiB/s
> >> Average speed: 43.6MiB/s
> >>
> >> 2) Random read:
> >> Speed: 30.6MiB/s, 30.9MiB/s, 30.5MiB/s
> >> Average speed: 30.6MiB/s
> >>
> >> 3) Sequential write:
> >> Speed: 44.1MiB/s, 45.9MiB/s, 44.2MiB/s
> >> Average speed: 44.7MiB/s
> >>
> >> 4) Random write:
> >> Speed: 45.1MiB/s, 43.3MiB/s, 42.4MiB/s
> >> Average speed: 43.6MiB/s
> >>
> >> Form above data, we can see the MMC software queue can help to improve the
> >> performance obviously.
> >>
> >> Any comments are welcome. Thanks a lot.
> >>
> >> Changes from v2:
> >>  - Remove reference to 'struct cqhci_host' and 'struct cqhci_slot',
> >>  instead adding 'struct sqhci_host', which is only used by software queue.
> >>
> >> Changes from v1:
> >>  - Add request_done ops for sdhci_ops.
> >>  - Replace virtual command queue with software queue for functions and
> >>  variables.
> >>  - Rename the software queue file and add sqhci.h header file.
> >
> > Do you have any comments for this patch set except the random config
> > building issue that will be fixed in the next version? Thanks.
>
> Pedantically, swhci is not a host controller interface, so the name still
> seems inappropriate. Otherwise I haven't had time to look at it, sorry.

OK. I will talk with Ulf to think about a good name. Thanks.

-- 
Baolin Wang
Best Regards