| Message ID | 03705222390bfa3b48ad7658f693fc0fc030b3ae.1660596679.git.christophe.jaillet@wanadoo.fr (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v2] scsi: target: Save a few cycles in transport_lookup_[cmd|tmr]_lun() | expand |
On 8/15/22 13:52, Christophe JAILLET wrote: > Use percpu_ref_tryget_live_rcu() instead of percpu_ref_tryget_live() to > save a few cycles when it is known that the rcu lock is already > taken/released. > > Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> > --- do you have a quantitative data that shows actual savings of cycles? -ck
Le 16/08/2022 à 08:06, Chaitanya Kulkarni a écrit : > On 8/15/22 13:52, Christophe JAILLET wrote: >> Use percpu_ref_tryget_live_rcu() instead of percpu_ref_tryget_live() to >> save a few cycles when it is known that the rcu lock is already >> taken/released. >> >> Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> >> --- > do you have a quantitative data that shows actual savings of cycles? > > -ck > Some numbers were given for io_uring by the one who introduced percpu_ref_tryget_live_rcu(). See [1]. I don't have specific numbers for the patch against scsi. CJ [1]: https://lore.kernel.org/linux-kernel/cover.1634822969.git.asml.silence@gmail.com/
diff --git a/drivers/target/target_core_device.c b/drivers/target/target_core_device.c index b7f16ee8aa0e..76c6613a1da7 100644 --- a/drivers/target/target_core_device.c +++ b/drivers/target/target_core_device.c @@ -77,7 +77,7 @@ transport_lookup_cmd_lun(struct se_cmd *se_cmd) se_lun = deve->se_lun; - if (!percpu_ref_tryget_live(&se_lun->lun_ref)) { + if (!percpu_ref_tryget_live_rcu(&se_lun->lun_ref)) { se_lun = NULL; goto out_unlock; } @@ -154,7 +154,7 @@ int transport_lookup_tmr_lun(struct se_cmd *se_cmd) if (deve) { se_lun = deve->se_lun; - if (!percpu_ref_tryget_live(&se_lun->lun_ref)) { + if (!percpu_ref_tryget_live_rcu(&se_lun->lun_ref)) { se_lun = NULL; goto out_unlock; }
Use percpu_ref_tryget_live_rcu() instead of percpu_ref_tryget_live() to save a few cycles when it is known that the rcu lock is already taken/released. Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr> --- Change in v2: * sync with -next v1: * https://lore.kernel.org/all/e4a21bc607c39935cb98d4825cd63ba349820550.1635974637.git.christophe.jaillet@wanadoo.fr/ --- drivers/target/target_core_device.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)