Re: [PATCH v3] target: Drop iSCSI use of mutex around max_cmd_sn increment

Nicholas A. Bellinger
2015-08-03T06:21:47Z

On Thu, 2015-07-23 at 14:53 -0700, Spencer Baugh wrote:
> From: Roland Dreier <roland@purestorage.com>
>
> In a performance profile, taking a mutex in iscsit_increment_maxcmdsn()
> shows up very high. However taking a mutex around "sess->max_cmd_sn += 1"
> seems pretty silly: we're not serializing against other contexts in
> any useful way.
>
> I did a quick audit and there don't appear to be any other places that
> use max_cmd_sn within the mutex more than once, so this lock can't be
> providing any useful serialization.
>
> v2: Get correct values for logging
> v3: Fix whitespace damage
>
> Signed-off-by: Roland Dreier <roland@purestorage.com>
> Signed-off-by: Spencer Baugh <sbaugh@catern.com>
> ---
> drivers/target/iscsi/iscsi_target.c | 18 +++++++++---------
> drivers/target/iscsi/iscsi_target_configfs.c | 6 ++++--
> drivers/target/iscsi/iscsi_target_device.c | 7 ++-----
> drivers/target/iscsi/iscsi_target_login.c | 2 +-
> drivers/target/iscsi/iscsi_target_nego.c | 9 +++------
> drivers/target/iscsi/iscsi_target_tmr.c | 2 +-
> drivers/target/iscsi/iscsi_target_util.c | 7 ++++---
> include/target/iscsi/iscsi_target_core.h | 2 +-
> 8 files changed, 25 insertions(+), 28 deletions(-)
>

A nice optimization for iscsi-target + ib_isert on this patch.

Applied to target-pending/for-next.

Thanks Roland & Co.