2021-11-03 21:33:34

by Christophe JAILLET

Subject: [PATCH] aio: Save a few cycles in 'lookup_ioctx()'

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 <[email protected]>
---
fs/aio.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/aio.c b/fs/aio.c
index 9c81cf611d65..d189ea13e10a 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1062,7 +1062,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
id = array_index_nospec(id, table->nr);
ctx = rcu_dereference(table->table[id]);
if (ctx && ctx->user_id == ctx_id) {
- if (percpu_ref_tryget_live(&ctx->users))
+ if (percpu_ref_tryget_live_rcu(&ctx->users))
ret = ctx;
}
out:
--
2.30.2

2022-08-12 05:33:32

by Christophe JAILLET

Subject: Re: [PATCH] aio: Save a few cycles in 'lookup_ioctx()'

Le 03/11/2021 à 22:31, Christophe JAILLET a écrit :
> 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 <[email protected]>
> ---
> fs/aio.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 9c81cf611d65..d189ea13e10a 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -1062,7 +1062,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
> id = array_index_nospec(id, table->nr);
> ctx = rcu_dereference(table->table[id]);
> if (ctx && ctx->user_id == ctx_id) {
> - if (percpu_ref_tryget_live(&ctx->users))
> + if (percpu_ref_tryget_live_rcu(&ctx->users))
> ret = ctx;
> }
> out:


Hi,
gentle reminder.

Is this patch useful?
When I first posted it, percpu_ref_tryget_live_rcu() was really new.
Now it is part of linux since 5.16.

Saving a few cycles in a function with "lookup" in its name looks always
good to me.

CJ

2022-08-15 20:15:08

by Jeff Moyer

Subject: Re: [PATCH] aio: Save a few cycles in 'lookup_ioctx()'

Christophe JAILLET <[email protected]> writes:

> Le 03/11/2021 à 22:31, Christophe JAILLET a écrit :
>> 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 <[email protected]>
>> ---
>> fs/aio.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/fs/aio.c b/fs/aio.c
>> index 9c81cf611d65..d189ea13e10a 100644
>> --- a/fs/aio.c
>> +++ b/fs/aio.c
>> @@ -1062,7 +1062,7 @@ static struct kioctx *lookup_ioctx(unsigned long ctx_id)
>> id = array_index_nospec(id, table->nr);
>> ctx = rcu_dereference(table->table[id]);
>> if (ctx && ctx->user_id == ctx_id) {
>> - if (percpu_ref_tryget_live(&ctx->users))
>> + if (percpu_ref_tryget_live_rcu(&ctx->users))
>> ret = ctx;
>> }
>> out:
>
>
> Hi,
> gentle reminder.
>
> Is this patch useful?
> When I first posted it, percpu_ref_tryget_live_rcu() was really new.
> Now it is part of linux since 5.16.
>
> Saving a few cycles in a function with "lookup" in its name looks
> always good to me.

The patch looks fine to me.

Reviewed-by: Jeff Moyer <[email protected]>