From: Frederic Weisbecker <frederic@kernel.org>
To: Mukesh Ojha <quic_mojha@quicinc.com>
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
tglx@linutronix.de, paulmck@kernel.org, will@kernel.org,
dave@stgolabs.net
Subject: Re: [PATCH] softirq: Remove raise_softirq from tasklet_action_common()
Date: Wed, 9 Feb 2022 00:04:55 +0100 [thread overview]
Message-ID: <20220208230455.GA539926@lothringen> (raw)
In-Reply-To: <1644066805-17212-1-git-send-email-quic_mojha@quicinc.com>
On Sat, Feb 05, 2022 at 06:43:25PM +0530, Mukesh Ojha wrote:
> Think about a scenario when all other cores are in suspend
> and one core is only running ksoftirqd and it is because
> some client has invoked tasklet_hi_schedule() only once
> during that phase.
>
> tasklet_action_common() handles that softirq and marks the
> same softirq as pending again. And due to that core keeps
> running the softirq handler [1] forever and it is not able to
> go to suspend.
>
> We can get rid of raising softirq from tasklet handler.
>
> [1]
> <idle>-0 [003] 13058.769081: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13058.769085: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13058.769087: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13058.769091: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13058.769094: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13058.769097: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13058.769100: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13058.769103: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13058.769106: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13058.769109: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058923: softirq_entry vec=0 action=HI_SOFTIRQ
> ...
> ..
> ..
> ..
>
> <idle>-0 [003] 13059.058951: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058954: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13059.058957: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058960: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058963: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13059.058966: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058969: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058972: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13059.058975: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058978: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058981: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13059.058984: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058987: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058990: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13059.058993: softirq_exit vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.058996: softirq_entry vec=0 action=HI_SOFTIRQ
> <idle>-0 [003] 13059.059000: softirq_raise: vec=0 [action=HI_SOFTIRQ]
> <idle>-0 [003] 13059.059002: softirq_exit vec=0 action=HI_SOFTIRQ
>
> Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> ---
> kernel/softirq.c | 1 -
> 1 file changed, 1 deletion(-)
>
> diff --git a/kernel/softirq.c b/kernel/softirq.c
> index 41f4709..d3e6fb9 100644
> --- a/kernel/softirq.c
> +++ b/kernel/softirq.c
> @@ -795,7 +795,6 @@ static void tasklet_action_common(struct softirq_action *a,
> t->next = NULL;
> *tl_head->tail = t;
> tl_head->tail = &t->next;
> - __raise_softirq_irqoff(softirq_nr);
> local_irq_enable();
That requeue happens when the tasklet is already executing on some other CPU
or when it has been disabled through tasklet_disable().
So you can't just remove that line or you'll break everything.
It would be nice to identify which tasklet keeps being requeued. Is it because
something called tasklet_disable() to it and never called back tasklet_enable() ?
Thanks.
next prev parent reply other threads:[~2022-02-09 2:39 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-05 13:13 [PATCH] softirq: Remove raise_softirq from tasklet_action_common() Mukesh Ojha
2022-02-08 13:40 ` Mukesh Ojha
2022-02-08 23:04 ` Frederic Weisbecker [this message]
2022-02-21 11:18 ` Mukesh Ojha
2022-02-23 15:50 ` Mukesh Ojha
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