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a=wKuvFiaSGQ0qltdbU6+NXLB8nM8=:19 a=Ol13hO9ccFRV9qXi2t6ftBPywas=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=yJojWOMRYYMA:10 a=GoEa3M9JfhUA:10 a=VwQbUJbxAAAA:8 a=N54-gffFAAAA:8 a=JfrnYn6hAAAA:8 a=20KFwNOVAAAA:8 a=yPCof4ZbAAAA:8 a=Bj0yz4kmN1o_EVaBk7MA:9 a=QEXdDO2ut3YA:10 a=1CNFftbPRP8L7MoqJWF3:22 cc=ntf awl=host:12084 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwOTA4MDE2NSBTYWx0ZWRfX9XkH7/v/8Byu 6ch0HJpZn4ywLg7ixBoFmd4rtgx764o5d08iNFKsE+tDoaluUF+C0kGYES3kaBjm9e9S9AqZmus F/HTlZyn5ZGXHzuOl88TgAi88dtzd+lkM0FZODcRO0ctghlCbg7HJldZEdXibn400CyXUNpj0Ha e3wHFva8uUK48LEesXez9PTh4KMk3xKm0Ee0s3fGWOHNxohiS/erB03z+yoiZWeSW7UggxiXsg8 e58kxlA1YuoqiUikrygzUHsP3OjPg4DZxGxQVYkfOzxkpgUQcJUpVGf1/UkSB1xdF5CsczX+qN8 6EexJqCXXtj8pDdzM//evXML6loF+sol/3GwYQ4BSR4djOVw2hzTkEBvHxseLdqbseIgQv+Z4P9 JAe2xADConExOMSQ52RpCXgcxTU0aQ== X-Proofpoint-GUID: 6NynjClbj4_TxWHEdi1vhA-vFBGwP6Uo X-Proofpoint-ORIG-GUID: 6NynjClbj4_TxWHEdi1vhA-vFBGwP6Uo On 10/09/2025 22:32, Bart Van Assche wrote: > The SCSI core uses the budget map to enforce the cmd_per_lun limit. That's not strictly true, as I mentioned in https://lore.kernel.org/linux-scsi/e7708546-c001-4f31-b895-69720755c3ac@acm.org/T/#m16d3bf6266faefee60addb48ae4b5cdd65e90a68 cmd_per_lun may be completely ignored by the LLD setting its own sdev queue depth. > That limit cannot be exceeded if host->cmd_per_lun >= host->can_queue Can host->cmd_per_lun > host->can_queue ever be true? > and if the host tag set is shared across all hardware queues. Sure, but what about single HW queue scenario? We should also enforce host->cmd_per_lun <= host->can_queue && sdev->max_queue_depth <= host->can_queue for that, right? Most/all single HW queue SCSI LLDs do not set .host_tagset (even though they could). > Since scsi_mq_get_budget() shows up in all CPU profiles for fast SCSI > devices, do not allocate a budget map if cmd_per_lun >= can_queue and > if the host tag set is shared across all hardware queues. > > On my UFS 4 test setup this patch improves IOPS by 1% and reduces the > time spent in scsi_mq_get_budget() from 0.22% to 0.01%. > > Cc: Jens Axboe > Cc: Christoph Hellwig > Cc: Ming Lei > Cc: John Garry > Signed-off-by: Bart Van Assche > --- > drivers/scsi/scsi.c | 7 ++++- > drivers/scsi/scsi_lib.c | 60 +++++++++++++++++++++++++++++++++----- > drivers/scsi/scsi_scan.c | 11 ++++++- > include/scsi/scsi_device.h | 5 +--- > 4 files changed, 70 insertions(+), 13 deletions(-) > > diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c > index 9a0f467264b3..06066b694d8a 100644 > --- a/drivers/scsi/scsi.c > +++ b/drivers/scsi/scsi.c > @@ -216,6 +216,8 @@ int scsi_device_max_queue_depth(struct scsi_device *sdev) > */ > int scsi_change_queue_depth(struct scsi_device *sdev, int depth) > { > + struct Scsi_Host *shost = sdev->host; > + > depth = min_t(int, depth, scsi_device_max_queue_depth(sdev)); > > if (depth > 0) { > @@ -226,7 +228,10 @@ int scsi_change_queue_depth(struct scsi_device *sdev, int depth) > if (sdev->request_queue) > blk_set_queue_depth(sdev->request_queue, depth); > > - sbitmap_resize(&sdev->budget_map, sdev->queue_depth); > + if (shost->host_tagset && depth >= shost->can_queue) > + sbitmap_free(&sdev->budget_map); eh, what happens if we call this twice? > + else > + sbitmap_resize(&sdev->budget_map, sdev->queue_depth); what if we set queue_depth = shost->can_queue (and free the budget map) and then later set lower than shost->can_queue (and try to reference the budget map)? > > return sdev->queue_depth; > } > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index 0c65ecfedfbd..c546514d1049 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -396,7 +396,8 @@ void scsi_device_unbusy(struct scsi_device *sdev, struct scsi_cmnd *cmd) > if (starget->can_queue > 0) > atomic_dec(&starget->target_busy); > > - sbitmap_put(&sdev->budget_map, cmd->budget_token); > + if (sdev->budget_map.map) > + sbitmap_put(&sdev->budget_map, cmd->budget_token); > cmd->budget_token = -1; > } > > @@ -445,6 +446,47 @@ static void scsi_single_lun_run(struct scsi_device *current_sdev) > spin_unlock_irqrestore(shost->host_lock, flags); > } > > +struct sdev_in_flight_data { > + const struct scsi_device *sdev; > + int count; > +}; > + > +static bool scsi_device_check_in_flight(struct request *rq, void *data) so this does not check the cmd state (like scsi_host_check_in_flight() does), but it uses the same naming (scsi_xxx_check_in_flight) > +{ > + struct scsi_cmnd *cmd = blk_mq_rq_to_pdu(rq); > + struct sdev_in_flight_data *sifd = data; > + > + if (cmd->device == sifd->sdev) > + sifd->count++; > + > + return true; > +} > + > +/** > + * scsi_device_busy() - Number of commands allocated for a SCSI device > + * @sdev: SCSI device. > + * > + * Note: There is a subtle difference between this function and > + * scsi_host_busy(). scsi_host_busy() counts the number of commands that have > + * been started. This function counts the number of commands that have been > + * allocated. At least the UFS driver depends on this function counting commands > + * that have already been allocated but that have not yet been started. > + */ > +int scsi_device_busy(const struct scsi_device *sdev) > +{ > + struct sdev_in_flight_data sifd = { .sdev = sdev }; > + struct blk_mq_tag_set *set = &sdev->host->tag_set; > + > + if (sdev->budget_map.map) I really dislike these checks > + return sbitmap_weight(&sdev->budget_map); > + if (WARN_ON_ONCE(!set->shared_tags)) > + return 0; > + blk_mq_all_tag_iter(set->shared_tags, scsi_device_check_in_flight, > + &sifd); > + return sifd.count; > +} > +EXPORT_SYMBOL(scsi_device_busy); > + > static inline bool scsi_device_is_busy(struct scsi_device *sdev) > { > if (scsi_device_busy(sdev) >= sdev->queue_depth) > @@ -1358,11 +1400,13 @@ scsi_device_state_check(struct scsi_device *sdev, struct request *req) > static inline int scsi_dev_queue_ready(struct request_queue *q, > struct scsi_device *sdev) > { > - int token; > + int token = INT_MAX; > > - token = sbitmap_get(&sdev->budget_map); > - if (token < 0) > - return -1; > + if (sdev->budget_map.map) { this can race with a call to scsi_change_queue_depth() (which may free sdev->budget_map.map), right? scsi_change_queue_depth() does not seem to do any queue freezing. > + token = sbitmap_get(&sdev->budget_map); > + if (token < 0) > + return -1; > + } > thanks, John