* Re: [PATCH 3/4] irq_work: Slightly simplify IRQ_WORK_PENDING clearing
[not found] ` <20191108160858.31665-4-frederic@kernel.org>
@ 2019-11-12 20:27 ` Leonard Crestez
2019-11-13 0:22 ` Frederic Weisbecker
0 siblings, 1 reply; 2+ messages in thread
From: Leonard Crestez @ 2019-11-12 20:27 UTC (permalink / raw)
To: Frederic Weisbecker
Cc: Peter Zijlstra, Ingo Molnar, LKML, Paul E . McKenney,
Thomas Gleixner, Viresh Kumar, linux-pm@vger.kernel.org,
Stephen Rothwell
On 08.11.2019 18:09, Frederic Weisbecker wrote:
> Instead of fetching the value of flags and perform an xchg() to clear
> a bit, just use atomic_fetch_andnot() that is more suitable to do that
> job in one operation while keeping the full ordering.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Ingo Molnar <mingo@kernel.org>
> ---
> kernel/irq_work.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 255454a48346..49c53f80a13a 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -34,7 +34,7 @@ static bool irq_work_claim(struct irq_work *work)
> oflags = atomic_fetch_or(IRQ_WORK_CLAIMED, &work->flags);
> /*
> * If the work is already pending, no need to raise the IPI.
> - * The pairing atomic_xchg() in irq_work_run() makes sure
> + * The pairing atomic_fetch_andnot() in irq_work_run() makes sure
> * everything we did before is visible.
> */
> if (oflags & IRQ_WORK_PENDING)
> @@ -135,7 +135,6 @@ static void irq_work_run_list(struct llist_head *list)
> {
> struct irq_work *work, *tmp;
> struct llist_node *llnode;
> - int flags;
>
> BUG_ON(!irqs_disabled());
>
> @@ -144,6 +143,7 @@ static void irq_work_run_list(struct llist_head *list)
>
> llnode = llist_del_all(list);
> llist_for_each_entry_safe(work, tmp, llnode, llnode) {
> + int flags;
> /*
> * Clear the PENDING bit, after this point the @work
> * can be re-used.
> @@ -151,8 +151,7 @@ static void irq_work_run_list(struct llist_head *list)
> * to claim that work don't rely on us to handle their data
> * while we are in the middle of the func.
> */
> - flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING;
> - atomic_xchg(&work->flags, flags);
> + flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
>
> work->func(work);
> /*
This breaks switching between cpufreq governors in linux-next on arm64
and various other stuff. The fix in this email doesn't compile:
https://lkml.org/lkml/2019/11/12/622
I assume you meant "&= ~" instead of "~=", this seems to work:
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 49c53f80a13a..828cc30774bc 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -156,10 +156,11 @@ static void irq_work_run_list(struct llist_head *list)
work->func(work);
/*
* Clear the BUSY bit and return to the free state if
* no-one else claimed it meanwhile.
*/
+ flags &= ~IRQ_WORK_PENDING;
(void)atomic_cmpxchg(&work->flags, flags, flags &
~IRQ_WORK_BUSY);
}
}
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH 3/4] irq_work: Slightly simplify IRQ_WORK_PENDING clearing
2019-11-12 20:27 ` [PATCH 3/4] irq_work: Slightly simplify IRQ_WORK_PENDING clearing Leonard Crestez
@ 2019-11-13 0:22 ` Frederic Weisbecker
0 siblings, 0 replies; 2+ messages in thread
From: Frederic Weisbecker @ 2019-11-13 0:22 UTC (permalink / raw)
To: Leonard Crestez
Cc: Peter Zijlstra, Ingo Molnar, LKML, Paul E . McKenney,
Thomas Gleixner, Viresh Kumar, linux-pm@vger.kernel.org,
Stephen Rothwell
On Tue, Nov 12, 2019 at 08:27:05PM +0000, Leonard Crestez wrote:
> On 08.11.2019 18:09, Frederic Weisbecker wrote:
> > Instead of fetching the value of flags and perform an xchg() to clear
> > a bit, just use atomic_fetch_andnot() that is more suitable to do that
> > job in one operation while keeping the full ordering.
> >
> > Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> > Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > ---
> > kernel/irq_work.c | 7 +++----
> > 1 file changed, 3 insertions(+), 4 deletions(-)
> >
> > diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> > index 255454a48346..49c53f80a13a 100644
> > --- a/kernel/irq_work.c
> > +++ b/kernel/irq_work.c
> > @@ -34,7 +34,7 @@ static bool irq_work_claim(struct irq_work *work)
> > oflags = atomic_fetch_or(IRQ_WORK_CLAIMED, &work->flags);
> > /*
> > * If the work is already pending, no need to raise the IPI.
> > - * The pairing atomic_xchg() in irq_work_run() makes sure
> > + * The pairing atomic_fetch_andnot() in irq_work_run() makes sure
> > * everything we did before is visible.
> > */
> > if (oflags & IRQ_WORK_PENDING)
> > @@ -135,7 +135,6 @@ static void irq_work_run_list(struct llist_head *list)
> > {
> > struct irq_work *work, *tmp;
> > struct llist_node *llnode;
> > - int flags;
> >
> > BUG_ON(!irqs_disabled());
> >
> > @@ -144,6 +143,7 @@ static void irq_work_run_list(struct llist_head *list)
> >
> > llnode = llist_del_all(list);
> > llist_for_each_entry_safe(work, tmp, llnode, llnode) {
> > + int flags;
> > /*
> > * Clear the PENDING bit, after this point the @work
> > * can be re-used.
> > @@ -151,8 +151,7 @@ static void irq_work_run_list(struct llist_head *list)
> > * to claim that work don't rely on us to handle their data
> > * while we are in the middle of the func.
> > */
> > - flags = atomic_read(&work->flags) & ~IRQ_WORK_PENDING;
> > - atomic_xchg(&work->flags, flags);
> > + flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
> >
> > work->func(work);
> > /*
>
> This breaks switching between cpufreq governors in linux-next on arm64
> and various other stuff. The fix in this email doesn't compile:
>
> https://lkml.org/lkml/2019/11/12/622
>
> I assume you meant "&= ~" instead of "~=", this seems to work:
Indeed, duh again!
I still think that ~= would be nice to have though...
Thanks!
>
> diff --git a/kernel/irq_work.c b/kernel/irq_work.c
> index 49c53f80a13a..828cc30774bc 100644
> --- a/kernel/irq_work.c
> +++ b/kernel/irq_work.c
> @@ -156,10 +156,11 @@ static void irq_work_run_list(struct llist_head *list)
> work->func(work);
> /*
> * Clear the BUSY bit and return to the free state if
> * no-one else claimed it meanwhile.
> */
> + flags &= ~IRQ_WORK_PENDING;
> (void)atomic_cmpxchg(&work->flags, flags, flags &
> ~IRQ_WORK_BUSY);
> }
> }
^ permalink raw reply [flat|nested] 2+ messages in thread
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2019-11-12 20:27 ` [PATCH 3/4] irq_work: Slightly simplify IRQ_WORK_PENDING clearing Leonard Crestez
2019-11-13 0:22 ` Frederic Weisbecker
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