| Message ID | 20230118225447.2809787-1-bvanassche@acm.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Add support for segments smaller than one page | expand |
On 1/18/23 3:54?PM, Bart Van Assche wrote: > Hi Jens, > > Several embedded storage controllers need support for DMA segments that are > smaller than the size of one virtual memory page. Hence this patch series. > Please consider this patch series for the next merge window. Before any real reviews are done, I have to ask "why?". This is pretty hairy code in the middle of the fast path for some obscure controller. Why would anyone ship that with > 4k page sizes rather than ship it with a controller that is sane?
On 1/18/23 17:18, Jens Axboe wrote: > On 1/18/23 3:54?PM, Bart Van Assche wrote: >> Hi Jens, >> >> Several embedded storage controllers need support for DMA segments that are >> smaller than the size of one virtual memory page. Hence this patch series. >> Please consider this patch series for the next merge window. > > Before any real reviews are done, I have to ask "why?". This is pretty > hairy code in the middle of the fast path for some obscure controller. > Why would anyone ship that with > 4k page sizes rather than ship it with > a controller that is sane? Hi Jens, The new config variable CONFIG_BLK_SUB_PAGE_SEGMENTS has been introduced to make sure that the hot path is *not* affected if that config variable is disabled. Regarding the question "why": the Google Android team would like to improve performance by switching from 4 KiB pages to 16 KiB pages. One of the widely used UFS controllers (Exynos) has a maximum segment size of 4 KiB. Hence this patch series. This patch series is not only useful for phones but also for Tesla cars since Tesla cars use an Exynos UFS controller. A contributor to the MMC driver told me that this patch series would allow to simplify the MMC driver significantly (I have not yet double checked this). Bart.
Hi Jens, Several embedded storage controllers need support for DMA segments that are smaller than the size of one virtual memory page. Hence this patch series. Please consider this patch series for the next merge window. Thanks, Bart. Changes compared to v2: - For SCSI drivers, only set flag QUEUE_FLAG_SUB_PAGE_SEGMENTS if necessary. - In the scsi_debug patch, sorted kernel module parameters alphabetically. Only set flag QUEUE_FLAG_SUB_PAGE_SEGMENTS if necessary. - Added a patch for the UFS Exynos driver that enables CONFIG_BLK_SUB_PAGE_SEGMENTS if the page size exceeds 4 KiB. Changes compared to v1: - Added a CONFIG variable that controls whether or not small segment support is enabled. - Improved patch descriptions. Bart Van Assche (9): block: Introduce QUEUE_FLAG_SUB_PAGE_SEGMENTS and CONFIG_BLK_SUB_PAGE_SEGMENTS block: Support configuring limits below the page size block: Support submitting passthrough requests with small segments block: Add support for filesystem requests and small segments block: Add support for small segments in blk_rq_map_user_iov() scsi_debug: Support configuring the maximum segment size null_blk: Support configuring the maximum segment size scsi: core: Set BLK_SUB_PAGE_SEGMENTS for small max_segment_size values scsi: ufs: exynos: Select CONFIG_BLK_SUB_PAGE_SEGMENTS for lage page sizes block/Kconfig | 9 +++++++ block/blk-map.c | 43 ++++++++++++++++++++++++++----- block/blk-merge.c | 6 +++-- block/blk-mq.c | 2 ++ block/blk-settings.c | 20 ++++++++------ block/blk.h | 22 +++++++++++----- drivers/block/null_blk/main.c | 21 ++++++++++++--- drivers/block/null_blk/null_blk.h | 1 + drivers/scsi/scsi_debug.c | 15 +++++++++++ drivers/scsi/scsi_lib.c | 3 +++ drivers/ufs/host/Kconfig | 1 + include/linux/blkdev.h | 7 +++++ 12 files changed, 125 insertions(+), 25 deletions(-)