From: Frederic Weisbecker <frederic@kernel.org>
To: Qais Yousef <qais.yousef@arm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
LKML <linux-kernel@vger.kernel.org>,
Tony Luck <tony.luck@intel.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Paul Mackerras <paulus@samba.org>,
Christian Borntraeger <borntraeger@de.ibm.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Heiko Carstens <hca@linux.ibm.com>
Subject: Re: [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation
Date: Tue, 29 Dec 2020 15:30:54 +0100 [thread overview]
Message-ID: <20201229143054.GC21613@lothringen> (raw)
In-Reply-To: <20201229141231.c2ppmjucxxbz5j5h@e107158-lin>
On Tue, Dec 29, 2020 at 02:12:31PM +0000, Qais Yousef wrote:
> On 12/29/20 14:41, Frederic Weisbecker wrote:
> > > > -void vtime_account_irq(struct task_struct *tsk)
> > > > +void vtime_account_irq(struct task_struct *tsk, unsigned int offset)
> > > > {
> > > > - if (hardirq_count()) {
> > > > + unsigned int pc = preempt_count() - offset;
> > > > +
> > > > + if (pc & HARDIRQ_OFFSET) {
> > >
> > > Shouldn't this be HARDIRQ_MASK like above?
> >
> > In the rare cases of nested hardirqs happening with broken drivers, Only the outer hardirq
> > does matter. All the time spent in the inner hardirqs is included in the outer
> > one.
>
> Ah I see. The original code was doing hardirq_count(), which apparently wasn't
> right either.
>
> Shouldn't it be pc == HARDIRQ_OFFSET then? All odd nest counts will trigger
> this otherwise, and IIUC we want this to trigger once on first entry only.
Right but we must also handle hardirqs interrupting either preempt disabled sections
or softirq servicing/disabled section.
3 stacking hardirqs should be rare enough that we don't really care. In the
worst case we are going to account the third IRQ seperately. Not a correctness
issue, just a rare unoptimized case.
>
> Thanks
>
> --
> Qais Yousef
next prev parent reply other threads:[~2020-12-29 14:31 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-02 11:57 [PATCH 0/5] irq: Reorder time handling against HARDIRQ_OFFSET on IRQ entry v3 Frederic Weisbecker
2020-12-02 11:57 ` [PATCH 1/5] sched/cputime: Remove symbol exports from IRQ time accounting Frederic Weisbecker
2020-12-02 19:23 ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
2020-12-02 19:28 ` [PATCH 1/5] " Christian Borntraeger
2020-12-02 11:57 ` [PATCH 2/5] s390/vtime: Use the generic IRQ entry accounting Frederic Weisbecker
2020-12-02 19:23 ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
2020-12-02 19:34 ` [PATCH 2/5] " Christian Borntraeger
2020-12-02 11:57 ` [PATCH 3/5] sched/vtime: Consolidate IRQ time accounting Frederic Weisbecker
2020-12-02 19:23 ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
2020-12-02 11:57 ` [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation Frederic Weisbecker
2020-12-02 12:36 ` Peter Zijlstra
2020-12-02 19:23 ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
2020-12-28 2:15 ` [PATCH 4/5] " Qais Yousef
2020-12-29 13:41 ` Frederic Weisbecker
2020-12-29 14:12 ` Qais Yousef
2020-12-29 14:30 ` Frederic Weisbecker [this message]
2020-12-29 15:58 ` Qais Yousef
2020-12-02 11:57 ` [PATCH 5/5] irq: Call tick_irq_enter() inside HARDIRQ_OFFSET Frederic Weisbecker
2020-12-02 19:23 ` [tip: irq/core] " tip-bot2 for Frederic Weisbecker
-- strict thread matches above, loose matches on Subject: below --
2020-12-01 0:12 [PATCH 0/5] irq: Reorder time handling against HARDIRQ_OFFSET on IRQ entry v2 Frederic Weisbecker
2020-12-01 0:12 ` [PATCH 4/5] irqtime: Move irqtime entry accounting after irq offset incrementation Frederic Weisbecker
2020-12-01 9:20 ` Peter Zijlstra
2020-12-01 11:23 ` Frederic Weisbecker
2020-12-01 11:33 ` Thomas Gleixner
2020-12-01 11:40 ` Frederic Weisbecker
2020-12-01 13:34 ` Thomas Gleixner
2020-12-01 14:35 ` Frederic Weisbecker
2020-12-01 15:01 ` Peter Zijlstra
2020-12-01 15:53 ` Thomas Gleixner
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