iorequest_cnt and iodone_cnt are updated on every command dispatch and completion, often from different CPUs on high queue depth workloads. Using adjacent atomic_t fields caused cache line contention between the submission and completion paths. Represent these statistics with struct percpu_counter so increments are mostly local to each CPU, avoiding false sharing without growing struct scsi_device further for cache-line padding. Suggested-by: Bart Van Assche Signed-off-by: Sumit Saxena --- drivers/scsi/scsi_error.c | 2 +- drivers/scsi/scsi_lib.c | 8 ++++---- drivers/scsi/scsi_scan.c | 9 +++++++++ drivers/scsi/scsi_sysfs.c | 27 +++++++++++++++++++++++---- include/scsi/scsi_device.h | 5 +++-- 5 files changed, 40 insertions(+), 11 deletions(-) diff --git a/drivers/scsi/scsi_error.c b/drivers/scsi/scsi_error.c index 147127fb4db9..c7424ce92f3e 100644 --- a/drivers/scsi/scsi_error.c +++ b/drivers/scsi/scsi_error.c @@ -370,7 +370,7 @@ enum blk_eh_timer_return scsi_timeout(struct request *req) */ if (test_and_set_bit(SCMD_STATE_COMPLETE, &scmd->state)) return BLK_EH_DONE; - atomic_inc(&scmd->device->iodone_cnt); + percpu_counter_inc(&scmd->device->iodone_cnt); if (scsi_abort_command(scmd) != SUCCESS) { set_host_byte(scmd, DID_TIME_OUT); scsi_eh_scmd_add(scmd); diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c index 6e8c7a42603e..0b05cb63f630 100644 --- a/drivers/scsi/scsi_lib.c +++ b/drivers/scsi/scsi_lib.c @@ -1554,7 +1554,7 @@ static void scsi_complete(struct request *rq) INIT_LIST_HEAD(&cmd->eh_entry); - atomic_inc(&cmd->device->iodone_cnt); + percpu_counter_inc(&cmd->device->iodone_cnt); if (cmd->result) atomic_inc(&cmd->device->ioerr_cnt); @@ -1592,7 +1592,7 @@ static enum scsi_qc_status scsi_dispatch_cmd(struct scsi_cmnd *cmd) struct Scsi_Host *host = cmd->device->host; int rtn = 0; - atomic_inc(&cmd->device->iorequest_cnt); + percpu_counter_inc(&cmd->device->iorequest_cnt); /* check if the device is still usable */ if (unlikely(cmd->device->sdev_state == SDEV_DEL)) { @@ -1614,7 +1614,7 @@ static enum scsi_qc_status scsi_dispatch_cmd(struct scsi_cmnd *cmd) */ SCSI_LOG_MLQUEUE(3, scmd_printk(KERN_INFO, cmd, "queuecommand : device blocked\n")); - atomic_dec(&cmd->device->iorequest_cnt); + percpu_counter_dec(&cmd->device->iorequest_cnt); return SCSI_MLQUEUE_DEVICE_BUSY; } @@ -1647,7 +1647,7 @@ static enum scsi_qc_status scsi_dispatch_cmd(struct scsi_cmnd *cmd) trace_scsi_dispatch_cmd_start(cmd); rtn = host->hostt->queuecommand(host, cmd); if (rtn) { - atomic_dec(&cmd->device->iorequest_cnt); + percpu_counter_dec(&cmd->device->iorequest_cnt); trace_scsi_dispatch_cmd_error(cmd, rtn); if (rtn != SCSI_MLQUEUE_DEVICE_BUSY && rtn != SCSI_MLQUEUE_TARGET_BUSY) diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c index 9749a8dbe964..0b4fa89149af 100644 --- a/drivers/scsi/scsi_scan.c +++ b/drivers/scsi/scsi_scan.c @@ -351,6 +351,15 @@ static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget, scsi_sysfs_device_initialize(sdev); + ret = percpu_counter_init(&sdev->iorequest_cnt, 0, GFP_KERNEL); + if (ret) + goto out_device_destroy; + ret = percpu_counter_init(&sdev->iodone_cnt, 0, GFP_KERNEL); + if (ret) { + percpu_counter_destroy(&sdev->iorequest_cnt); + goto out_device_destroy; + } + if (scsi_device_is_pseudo_dev(sdev)) return sdev; diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c index dfc3559e7e04..1f5b2dc156a8 100644 --- a/drivers/scsi/scsi_sysfs.c +++ b/drivers/scsi/scsi_sysfs.c @@ -516,6 +516,10 @@ static void scsi_device_dev_release(struct device *dev) if (vpd_pgb7) kfree_rcu(vpd_pgb7, rcu); kfree(sdev->inquiry); + if (percpu_counter_initialized(&sdev->iodone_cnt)) + percpu_counter_destroy(&sdev->iodone_cnt); + if (percpu_counter_initialized(&sdev->iorequest_cnt)) + percpu_counter_destroy(&sdev->iorequest_cnt); kfree(sdev); if (parent) @@ -936,11 +940,26 @@ static ssize_t show_iostat_counterbits(struct device *dev, struct device_attribute *attr, char *buf) { - return snprintf(buf, 20, "%d\n", (int)sizeof(atomic_t) * 8); + /* + * iorequest_cnt and iodone_cnt are per-CPU sums (s64); ioerr_cnt and + * iotmo_cnt remain atomic_t. Report the widest counter for tools. + */ + return snprintf(buf, 20, "%zu\n", sizeof(s64) * 8); } static DEVICE_ATTR(iocounterbits, S_IRUGO, show_iostat_counterbits, NULL); +#define show_sdev_iostat_percpu(field) \ +static ssize_t \ +show_iostat_##field(struct device *dev, struct device_attribute *attr, \ + char *buf) \ +{ \ + struct scsi_device *sdev = to_scsi_device(dev); \ + unsigned long long count = percpu_counter_sum(&sdev->field); \ + return snprintf(buf, 20, "0x%llx\n", count); \ +} \ +static DEVICE_ATTR(field, 0444, show_iostat_##field, NULL) + #define show_sdev_iostat(field) \ static ssize_t \ show_iostat_##field(struct device *dev, struct device_attribute *attr, \ @@ -950,10 +969,10 @@ show_iostat_##field(struct device *dev, struct device_attribute *attr, \ unsigned long long count = atomic_read(&sdev->field); \ return snprintf(buf, 20, "0x%llx\n", count); \ } \ -static DEVICE_ATTR(field, S_IRUGO, show_iostat_##field, NULL) +static DEVICE_ATTR(field, 0444, show_iostat_##field, NULL) -show_sdev_iostat(iorequest_cnt); -show_sdev_iostat(iodone_cnt); +show_sdev_iostat_percpu(iorequest_cnt); +show_sdev_iostat_percpu(iodone_cnt); show_sdev_iostat(ioerr_cnt); show_sdev_iostat(iotmo_cnt); diff --git a/include/scsi/scsi_device.h b/include/scsi/scsi_device.h index 9c2a7bbe5891..ad80b500ced9 100644 --- a/include/scsi/scsi_device.h +++ b/include/scsi/scsi_device.h @@ -8,6 +8,7 @@ #include #include #include +#include #include struct bsg_device; @@ -271,8 +272,8 @@ struct scsi_device { unsigned int max_device_blocked; /* what device_blocked counts down from */ #define SCSI_DEFAULT_DEVICE_BLOCKED 3 - atomic_t iorequest_cnt; - atomic_t iodone_cnt; + struct percpu_counter iorequest_cnt; + struct percpu_counter iodone_cnt; atomic_t ioerr_cnt; atomic_t iotmo_cnt; -- 2.43.7