| Message ID | 20231114211804.1449162-1-bvanassche@acm.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Improve write performance for zoned UFS devices | expand |
As this keeps getting reposted: I still think it is a very bad idea to add this amount of complexity to the SCSI code, for a model that can't work for the general case and diverges from the established NVMe model. So I do not thing we should support this.
On 11/26/23 23:09, Christoph Hellwig wrote: > I still think it is a very bad idea to add this amount of complexity to > the SCSI code, for a model that can't work for the general case and > diverges from the established NVMe model. Hi Christoph, Here is some additional background information: * UFS vendors prefer the SCSI command set because they combine it with the M-PHY transport layer. This combination is more power efficient than NVMe over PCIe. According to the information I have available power consumption in the M-PHY hibernation state is lower than in the PCIe L2 state. I have not yet heard about any attempts to combine the NVMe command set with the M-PHY transport layer. Even if this would be possible, it would fragment the mobile storage market. This would increase the price of mobile storage devices which is undesirable. * I think that the "established NVMe model" in your email refers to the NVMe zone append command. As you know there is no zone append in the SCSI ZBC standard. * Using the software implementation of REQ_OP_ZONE_APPEND in drivers/scsi/sd_zbc.c is not an option. REQ_OP_ZONE_APPEND commands are serialized by that implementation. This serialization is unavoidable because a SCSI device may respond with a unit attention condition to any SCSI command. Hence, even if REQ_OP_ZONE_APPEND commands are submitted in order, these may be executed out-of-order. We do not want any serialization of SCSI commands because this has a significant negative performance impact on IOPS for UFS devices. The latest UFS devices support more than 300 K IOPS. * Serialization in the I/O scheduler of zoned writes also reduces IOPS more than what is acceptable. Hence the approach of this patch series to support pipelining of zoned writes even if no I/O scheduler has been configured. I think the amount of complexity introduced by this patch series in the SCSI core is reasonable. No new states are introduced in the SCSI core. A single call to a function that reorders pending SCSI commands is introduced in the SCSI error handler (scsi_call_prepare_resubmit()). Thanks, Bart.
On Mon, Nov 27, 2023 at 11:35:48AM -0800, Bart Van Assche wrote:
> Here is some additional background information:
I know the background. I also know that JEDEC did all this aginst
better judgement and knowing the situation. We should not give them
their carrot after they haven't even been interested in engaging.
On 11/28/23 04:53, Christoph Hellwig wrote: > I know the background. I also know that JEDEC did all this aginst > better judgement and knowing the situation. We should not give them > their carrot after they haven't even been interested in engaging. That statement is overly negative. The JEDEC Zoned Storage for UFS standard has been published last week [1]. It can be downloaded by anyone for free after having created a JEDEC account, which is also free. As one can see in this standard, nothing excludes using a zone append command. Once T10 standardizes a zone append command, it can be implemented by UFS vendors. However, I do not know whether T10 plans to standardize a zone append command. Bart. [1] https://www.jedec.org/system/files/docs/JESD220-5.pdf
Hi Martin, This patch series improves small write IOPS by a factor of four (+300%) for zoned UFS devices on my test setup with an UFSHCI 3.0 controller. Please consider this patch series for the next merge window. Thank you, Bart. Changes compared to v14: - Removed the drivers/scsi/Kconfig.kunit and drivers/scsi/Makefile.kunit files. Instead, modified drivers/scsi/Kconfig and added #include "*_test.c" directives in the appropriate .c files. Removed the EXPORT_SYMBOL() directives that were added to make the unit tests link. - Fixed a double free in a unit test. Changes compared to v13: - Reworked patch "block: Preserve the order of requeued zoned writes". - Addressed a performance concern by removing the eh_needs_prepare_resubmit SCSI driver callback and by introducing the SCSI host template flag .needs_prepare_resubmit instead. - Added a patch that adds a 'host' argument to scsi_eh_flush_done_q(). - Made the code in unit tests less repetitive. Changes compared to v12: - Added two new patches: "block: Preserve the order of requeued zoned writes" and "scsi: sd: Add a unit test for sd_cmp_sector()" - Restricted the number of zoned write retries. To my surprise I had to add "&& scmd->retries <= scmd->allowed" in the SCSI error handler to limit the number of retries. - In patch "scsi: ufs: Inform the block layer about write ordering", only set ELEVATOR_F_ZBD_SEQ_WRITE for zoned block devices. Changes compared to v11: - Fixed a NULL pointer dereference that happened when booting from an ATA device by adding an scmd->device != NULL check in scsi_needs_preparation(). - Updated Reviewed-by tags. Changes compared to v10: - Dropped the UFS MediaTek and HiSilicon patches because these are not correct and because it is safe to drop these patches. - Updated Acked-by / Reviewed-by tags. Changes compared to v9: - Introduced an additional scsi_driver callback: .eh_needs_prepare_resubmit(). - Renamed the scsi_debug kernel module parameter 'no_zone_write_lock' into 'preserves_write_order'. - Fixed an out-of-bounds access in the unit scsi_call_prepare_resubmit() unit test. - Wrapped ufshcd_auto_hibern8_update() calls in UFS host drivers with WARN_ON_ONCE() such that a kernel stack appears in case an error code is returned. - Elaborated a comment in the UFSHCI driver. Changes compared to v8: - Fixed handling of 'driver_preserves_write_order' and 'use_zone_write_lock' in blk_stack_limits(). - Added a comment in disk_set_zoned(). - Modified blk_req_needs_zone_write_lock() such that it returns false if q->limits.use_zone_write_lock is false. - Modified disk_clear_zone_settings() such that it clears q->limits.use_zone_write_lock. - Left out one change from the mq-deadline patch that became superfluous due to the blk_req_needs_zone_write_lock() change. - Modified scsi_call_prepare_resubmit() such that it only calls list_sort() if zoned writes have to be resubmitted for which zone write locking is disabled. - Added an additional unit test for scsi_call_prepare_resubmit(). - Modified the sorting code in the sd driver such that only those SCSI commands are sorted for which write locking is disabled. - Modified sd_zbc.c such that ELEVATOR_F_ZBD_SEQ_WRITE is only set if the write order is not preserved. - Included three patches for UFS host drivers that rework code that wrote directly to the auto-hibernation controller register. - Modified the UFS driver such that enabling auto-hibernation is not allowed if a zoned logical unit is present and if the controller operates in legacy mode. - Also in the UFS driver, simplified ufshcd_auto_hibern8_update(). Changes compared to v7: - Split the queue_limits member variable `use_zone_write_lock' into two member variables: `use_zone_write_lock' (set by disk_set_zoned()) and `driver_preserves_write_order' (set by the block driver or SCSI LLD). This should clear up the confusion about the purpose of this variable. - Moved the code for sorting SCSI commands by LBA from the SCSI error handler into the SCSI disk (sd) driver as requested by Christoph. Changes compared to v6: - Removed QUEUE_FLAG_NO_ZONE_WRITE_LOCK and instead introduced a flag in the request queue limits data structure. Changes compared to v5: - Renamed scsi_cmp_lba() into scsi_cmp_sector(). - Improved several source code comments. Changes compared to v4: - Dropped the patch that introduces the REQ_NO_ZONE_WRITE_LOCK flag. - Dropped the null_blk patch and added two scsi_debug patches instead. - Dropped the f2fs patch. - Split the patch for the UFS driver into two patches. - Modified several patch descriptions and source code comments. - Renamed dd_use_write_locking() into dd_use_zone_write_locking(). - Moved the list_sort() call from scsi_unjam_host() into scsi_eh_flush_done_q() such that sorting happens just before reinserting. - Removed the scsi_cmd_retry_allowed() call from scsi_check_sense() to make sure that the retry counter is adjusted once per retry instead of twice. Changes compared to v3: - Restored the patch that introduces QUEUE_FLAG_NO_ZONE_WRITE_LOCK. That patch had accidentally been left out from v2. - In patch "block: Introduce the flag REQ_NO_ZONE_WRITE_LOCK", improved the patch description and added the function blk_no_zone_write_lock(). - In patch "block/mq-deadline: Only use zone locking if necessary", moved the blk_queue_is_zoned() call into dd_use_write_locking(). - In patch "fs/f2fs: Disable zone write locking", set REQ_NO_ZONE_WRITE_LOCK from inside __bio_alloc() instead of in f2fs_submit_write_bio(). Changes compared to v2: - Renamed the request queue flag for disabling zone write locking. - Introduced a new request flag for disabling zone write locking. - Modified the mq-deadline scheduler such that zone write locking is only disabled if both flags are set. - Added an F2FS patch that sets the request flag for disabling zone write locking. - Only disable zone write locking in the UFS driver if auto-hibernation is disabled. Changes compared to v1: - Left out the patches that are already upstream. - Switched the approach in patch "scsi: Retry unaligned zoned writes" from retrying immediately to sending unaligned write commands to the SCSI error handler. Bart Van Assche (19): block: Introduce more member variables related to zone write locking block: Only use write locking if necessary block: Preserve the order of requeued zoned writes block/mq-deadline: Only use zone locking if necessary scsi: Pass SCSI host pointer to scsi_eh_flush_done_q() scsi: core: Introduce a mechanism for reordering requests in the error handler scsi: core: Add unit tests for scsi_call_prepare_resubmit() scsi: sd: Support sorting commands by LBA before resubmitting scsi: sd: Add a unit test for sd_cmp_sector() scsi: core: Retry unaligned zoned writes scsi: sd_zbc: Only require an I/O scheduler if needed scsi: scsi_debug: Add the preserves_write_order module parameter scsi: scsi_debug: Support injecting unaligned write errors scsi: ufs: hisi: Rework the code that disables auto-hibernation scsi: ufs: Rename ufshcd_auto_hibern8_enable() and make it static scsi: ufs: Change the return type of ufshcd_auto_hibern8_update() scsi: ufs: Simplify ufshcd_auto_hibern8_update() scsi: ufs: Forbid auto-hibernation without I/O scheduler scsi: ufs: Inform the block layer about write ordering block/blk-mq.c | 6 +- block/blk-settings.c | 15 ++ block/blk-zoned.c | 10 +- block/mq-deadline.c | 11 +- drivers/ata/libata-eh.c | 2 +- drivers/scsi/Kconfig | 10 ++ drivers/scsi/constants.c | 1 + drivers/scsi/libsas/sas_scsi_host.c | 2 +- drivers/scsi/scsi_debug.c | 21 ++- drivers/scsi/scsi_error.c | 77 ++++++++- drivers/scsi/scsi_error_test.c | 233 ++++++++++++++++++++++++++++ drivers/scsi/scsi_lib.c | 1 + drivers/scsi/sd.c | 44 ++++++ drivers/scsi/sd_test.c | 86 ++++++++++ drivers/scsi/sd_zbc.c | 4 +- drivers/ufs/core/ufs-sysfs.c | 2 +- drivers/ufs/core/ufshcd-priv.h | 1 - drivers/ufs/core/ufshcd.c | 119 +++++++++++--- drivers/ufs/host/ufs-hisi.c | 5 +- include/linux/blkdev.h | 10 ++ include/scsi/scsi.h | 1 + include/scsi/scsi_driver.h | 1 + include/scsi/scsi_eh.h | 3 +- include/scsi/scsi_host.h | 6 + include/ufs/ufshcd.h | 3 +- 25 files changed, 628 insertions(+), 46 deletions(-) create mode 100644 drivers/scsi/scsi_error_test.c create mode 100644 drivers/scsi/sd_test.c