On 4/27/18 9:31 AM, Bart Van Assche wrote: > On Fri, 2018-04-20 at 14:57 +0800, Ming Lei wrote: >> This patches removes the expensive atomic opeation on host-wide counter >> of .host_busy for scsi-mq, and it is observed that IOPS can be increased by >> 15% with this change in IO test over scsi_debug. >> >> >> Ming Lei (3): >> scsi: introduce scsi_host_busy() >> scsi: read host_busy via scsi_host_busy() >> scsi: avoid to hold host-wide counter of host_busy for scsi_mq >> >> drivers/scsi/advansys.c | 8 ++++---- >> drivers/scsi/hosts.c | 32 +++++++++++++++++++++++++++++++ >> drivers/scsi/libsas/sas_scsi_host.c | 4 ++-- >> drivers/scsi/megaraid/megaraid_sas_base.c | 2 +- >> drivers/scsi/mpt3sas/mpt3sas_base.c | 4 ++-- >> drivers/scsi/qlogicpti.c | 2 +- >> drivers/scsi/scsi.c | 2 +- >> drivers/scsi/scsi_error.c | 6 +++--- >> drivers/scsi/scsi_lib.c | 23 ++++++++++++++++------ >> drivers/scsi/scsi_sysfs.c | 2 +- >> include/scsi/scsi_host.h | 1 + >> 11 files changed, 65 insertions(+), 21 deletions(-)\ > > Hello Ming, > > From the MAINTAINERS file: > > SCSI SUBSYSTEM > M: "James E.J. Bottomley" <jejb@xxxxxxxxxxxxxxxxxx> > T: git git://git.kernel.org/pub/scm/linux/kernel/git/jejb/scsi.git > M: "Martin K. Petersen" <martin.petersen@xxxxxxxxxx> > T: git git://git.kernel.org/pub/scm/linux/kernel/git/mkp/scsi.git > L: linux-scsi@xxxxxxxxxxxxxxx > S: Maintained > F: Documentation/devicetree/bindings/scsi/ > F: drivers/scsi/ > F: include/scsi/ > > Hence my surprise when I saw that you sent this patch series to Jens instead > of James and Martin? Martin and James are both on the CC as well. For what it's worth, the patch seems like a good approach to me. To handle the case that Hannes was concerned about (older drivers doing internal command issue), I would suggest that those drivers get instrumented to include a inc/dec of the host busy count for internal commands that bypass the normal tagging. That means the mq case needs to be blk_mq_tagset_busy_iter(&shost->tag_set, scsi_host_check_in_flight, &in_flight); return in_flight.cnt + atomic_read(&shost->host_busy); The atomic read is basically free, once we get rid of the dirty of that variable on each IO. -- Jens Axboe
