When waiting for the completion of io, we need account iowait time. As
wait_for_completion() calls schedule_timeout(), which doesn't account
iowait time. While wait_for_completion_io() calls io_schedule_timeout(),
which will account iowait time.
So using wait_for_completion_io() instead of wait_for_completion()
when waiting for completion of io before exit_aio and io_destroy.
Signed-off-by: Xianting Tian <[email protected]>
---
fs/aio.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/aio.c b/fs/aio.c
index 91e7cc4..498b8a0 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -892,7 +892,7 @@ void exit_aio(struct mm_struct *mm)
if (!atomic_sub_and_test(skipped, &wait.count)) {
/* Wait until all IO for the context are done. */
- wait_for_completion(&wait.comp);
+ wait_for_completion_io(&wait.comp);
}
RCU_INIT_POINTER(mm->ioctx_table, NULL);
@@ -1400,7 +1400,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
* is destroyed.
*/
if (!ret)
- wait_for_completion(&wait.comp);
+ wait_for_completion_io(&wait.comp);
return ret;
}
--
1.8.3.1
On Wed 05-08-20 09:35:51, Xianting Tian wrote:
> When waiting for the completion of io, we need account iowait time. As
> wait_for_completion() calls schedule_timeout(), which doesn't account
> iowait time. While wait_for_completion_io() calls io_schedule_timeout(),
> which will account iowait time.
>
> So using wait_for_completion_io() instead of wait_for_completion()
> when waiting for completion of io before exit_aio and io_destroy.
>
> Signed-off-by: Xianting Tian <[email protected]>
Thanks for the patch! It looks good to me but IMO this is just scratching
the surface. E.g. for AIO we are mostly going to wait in read_events() by
wait_event_interruptible_hrtimeout() and *that* doesn't account as IO wait
either? Which is IMO far bigger misaccounting... The two case you fix seem
to be just rare cornercases so what they do isn't a big deal either way.
So I agree it may be worth it to properly account waiting for AIO but if
you want to do that, then please handle mainly the common cases in AIO
code.
Honza
> ---
> fs/aio.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/aio.c b/fs/aio.c
> index 91e7cc4..498b8a0 100644
> --- a/fs/aio.c
> +++ b/fs/aio.c
> @@ -892,7 +892,7 @@ void exit_aio(struct mm_struct *mm)
>
> if (!atomic_sub_and_test(skipped, &wait.count)) {
> /* Wait until all IO for the context are done. */
> - wait_for_completion(&wait.comp);
> + wait_for_completion_io(&wait.comp);
> }
>
> RCU_INIT_POINTER(mm->ioctx_table, NULL);
> @@ -1400,7 +1400,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
> * is destroyed.
> */
> if (!ret)
> - wait_for_completion(&wait.comp);
> + wait_for_completion_io(&wait.comp);
>
> return ret;
> }
> --
> 1.8.3.1
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
Hello!
On Wed 26-08-20 23:44:11, 田 wrote:
> thanks for your kindly reply,
> the normal wait path read_events()->wait_event_interruptible_hrtimeout(),
> which will call schedule(), it does not account IO wait time.
Not sure if there isn't some misunderstanding so I'll repeat what I've
said: Yes, above path will not account as IO wait time and IMO that is much
more common path which should be accounted as IO wait time. So I think that
without fixing that path, fixing cornercases like you did in your patch is
rather pointless.
Honza
> On 08/26/2020 21:23, Jan Kara wrote:
> On Wed 05-08-20 09:35:51, Xianting Tian wrote:
> > When waiting for the completion of io, we need account iowait time. As
> > wait_for_completion() calls schedule_timeout(), which doesn't account
> > iowait time. While wait_for_completion_io() calls io_schedule_timeout(),
> > which will account iowait time.
> >
> > So using wait_for_completion_io() instead of wait_for_completion()
> > when waiting for completion of io before exit_aio and io_destroy.
> >
> > Signed-off-by: Xianting Tian <[email protected]>
>
> Thanks for the patch! It looks good to me but IMO this is just scratching
> the surface. E.g. for AIO we are mostly going to wait in read_events() by
> wait_event_interruptible_hrtimeout() and *that* doesn't account as IO wait
> either? Which is IMO far bigger misaccounting... The two case you fix seem
> to be just rare cornercases so what they do isn't a big deal either way.
>
> So I agree it may be worth it to properly account waiting for AIO but if
> you want to do that, then please handle mainly the common cases in AIO
> code.
>
> Honza
>
> > ---
> > fs/aio.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/aio.c b/fs/aio.c
> > index 91e7cc4..498b8a0 100644
> > --- a/fs/aio.c
> > +++ b/fs/aio.c
> > @@ -892,7 +892,7 @@ void exit_aio(struct mm_struct *mm)
> >
> > if (!atomic_sub_and_test(skipped, &wait.count)) {
> > /* Wait until all IO for the context are done. */
> > - wait_for_completion(&wait.comp);
> > + wait_for_completion_io(&wait.comp);
> > }
> >
> > RCU_INIT_POINTER(mm->ioctx_table, NULL);
> > @@ -1400,7 +1400,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
> > * is destroyed.
> > */
> > if (!ret)
> > - wait_for_completion(&wait.comp);
> > + wait_for_completion_io(&wait.comp);
> >
> > return ret;
> > }
> > --
> > 1.8.3.1
> >
> --
> Jan Kara <[email protected]>
> SUSE Labs, CR
--
Jan Kara <[email protected]>
SUSE Labs, CR
Hi!
On Thu 27-08-20 16:28:37, 田 wrote:
> I understood what you said before:)
Good :)
> Totally agree with you, that we should fix the common path to make it to
> account IO wait time. Currently kernel only has io_wait_event(), which
> does not support timeout, maybe we need develop new interface like
> io_wait_event_hrtimeout(), then we can use it instead of
> wait_event_interruptible_hrtimeout()?
Yes, that's what I'd do.
Honza
>
> On 08/27/2020 15:55, Jan Kara wrote:
> Hello!
>
> On Wed 26-08-20 23:44:11, 田 wrote:
> > thanks for your kindly reply,
> > the normal wait path read_events()->wait_event_interruptible_hrtimeout(),
> > which will call schedule(), it does not account IO wait time.
>
> Not sure if there isn't some misunderstanding so I'll repeat what I've
> said: Yes, above path will not account as IO wait time and IMO that is much
> more common path which should be accounted as IO wait time. So I think that
> without fixing that path, fixing cornercases like you did in your patch is
> rather pointless.
>
> Honza
>
> > On 08/26/2020 21:23, Jan Kara wrote:
> > On Wed 05-08-20 09:35:51, Xianting Tian wrote:
> > > When waiting for the completion of io, we need account iowait time. As
> > > wait_for_completion() calls schedule_timeout(), which doesn't account
> > > iowait time. While wait_for_completion_io() calls io_schedule_timeout(),
> > > which will account iowait time.
> > >
> > > So using wait_for_completion_io() instead of wait_for_completion()
> > > when waiting for completion of io before exit_aio and io_destroy.
> > >
> > > Signed-off-by: Xianting Tian <[email protected]>
> >
> > Thanks for the patch! It looks good to me but IMO this is just scratching
> > the surface. E.g. for AIO we are mostly going to wait in read_events() by
> > wait_event_interruptible_hrtimeout() and *that* doesn't account as IO wait
> > either? Which is IMO far bigger misaccounting... The two case you fix seem
> > to be just rare cornercases so what they do isn't a big deal either way.
> >
> > So I agree it may be worth it to properly account waiting for AIO but if
> > you want to do that, then please handle mainly the common cases in AIO
> > code.
> >
> > Honza
> >
> > > ---
> > > fs/aio.c | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/fs/aio.c b/fs/aio.c
> > > index 91e7cc4..498b8a0 100644
> > > --- a/fs/aio.c
> > > +++ b/fs/aio.c
> > > @@ -892,7 +892,7 @@ void exit_aio(struct mm_struct *mm)
> > >
> > > if (!atomic_sub_and_test(skipped, &wait.count)) {
> > > /* Wait until all IO for the context are done. */
> > > - wait_for_completion(&wait.comp);
> > > + wait_for_completion_io(&wait.comp);
> > > }
> > >
> > > RCU_INIT_POINTER(mm->ioctx_table, NULL);
> > > @@ -1400,7 +1400,7 @@ static long read_events(struct kioctx *ctx, long min_nr, long nr,
> > > * is destroyed.
> > > */
> > > if (!ret)
> > > - wait_for_completion(&wait.comp);
> > > + wait_for_completion_io(&wait.comp);
> > >
> > > return ret;
> > > }
> > > --
> > > 1.8.3.1
> > >
> > --
> > Jan Kara <[email protected]>
> > SUSE Labs, CR
> --
> Jan Kara <[email protected]>
> SUSE Labs, CR
--
Jan Kara <[email protected]>
SUSE Labs, CR