From: Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
To: "jgross@suse.com" <jgross@suse.com>,
"julien@xen.org" <julien@xen.org>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: "sstabellini@kernel.org" <sstabellini@kernel.org>,
"wl@xen.org" <wl@xen.org>,
"andrew.cooper3@citrix.com" <andrew.cooper3@citrix.com>,
"ian.jackson@eu.citrix.com" <ian.jackson@eu.citrix.com>,
"george.dunlap@citrix.com" <george.dunlap@citrix.com>,
"dfaggioli@suse.com" <dfaggioli@suse.com>,
"jbeulich@suse.com" <jbeulich@suse.com>
Subject: Re: [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics.
Date: Fri, 12 Jun 2020 22:16:37 +0000 [thread overview]
Message-ID: <4ce2fd02329d3fa72f7b43d365056a8029996dbb.camel@epam.com> (raw)
In-Reply-To: <92d81acb-fd78-3483-68fb-f52c7bfb3d65@xen.org>
Hi Julien,
On Fri, 2020-06-12 at 13:45 +0100, Julien Grall wrote:
> Hi Volodymyr,
>
> On 12/06/2020 12:44, Volodymyr Babchuk wrote:
> > On Fri, 2020-06-12 at 06:57 +0200, Jürgen Groß wrote:
> > > On 12.06.20 02:22, Volodymyr Babchuk wrote:
> > > > As scheduler code now collects time spent in IRQ handlers and in
> > > > do_softirq(), we can present those values to userspace tools like
> > > > xentop, so system administrator can see how system behaves.
> > > >
> > > > We are updating counters only in sched_get_time_correction() function
> > > > to minimize number of taken spinlocks. As atomic_t is 32 bit wide, it
> > > > is not enough to store time with nanosecond precision. So we need to
> > > > use 64 bit variables and protect them with spinlock.
> > > >
> > > > Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
> > > > ---
> > > > xen/common/sched/core.c | 17 +++++++++++++++++
> > > > xen/common/sysctl.c | 1 +
> > > > xen/include/public/sysctl.h | 4 +++-
> > > > xen/include/xen/sched.h | 2 ++
> > > > 4 files changed, 23 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/xen/common/sched/core.c b/xen/common/sched/core.c
> > > > index a7294ff5c3..ee6b1d9161 100644
> > > > --- a/xen/common/sched/core.c
> > > > +++ b/xen/common/sched/core.c
> > > > @@ -95,6 +95,10 @@ static struct scheduler __read_mostly ops;
> > > >
> > > > static bool scheduler_active;
> > > >
> > > > +static DEFINE_SPINLOCK(sched_stat_lock);
> > > > +s_time_t sched_stat_irq_time;
> > > > +s_time_t sched_stat_hyp_time;
> > > > +
> > > > static void sched_set_affinity(
> > > > struct sched_unit *unit, const cpumask_t *hard, const cpumask_t *soft);
> > > >
> > > > @@ -994,9 +998,22 @@ s_time_t sched_get_time_correction(struct sched_unit *u)
> > > > break;
> > > > }
> > > >
> > > > + spin_lock_irqsave(&sched_stat_lock, flags);
> > > > + sched_stat_irq_time += irq;
> > > > + sched_stat_hyp_time += hyp;
> > > > + spin_unlock_irqrestore(&sched_stat_lock, flags);
> > >
> > > Please don't use a lock. Just use add_sized() instead which will add
> > > atomically.
> >
> > Looks like arm does not support 64 bit variables. >
> > Julien, I believe, this is armv7 limitation? Should armv8 work with 64-
> > bit atomics?
>
> 64-bit atomics can work on both Armv7 and Armv8 :). It just haven't been
> plumbed yet.
Wow, didn't know that armv7 is capable of that.
> I am happy to write a patch if you need atomic64_t or even a 64-bit
> add_sized().
That would be cool. Certainly. But looks like x86 code does not have
implementation for atomic64_t as well. So, there would be lots of
changes just for one use case. I don't know if it is worth it.
Let's finish discussion of other parts of the series. If it will appear
that atomic64_t is absolutely necessay, I'll return back to you.
Thanks for offer anyways.
next prev parent reply other threads:[~2020-06-12 22:17 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-12 0:22 [RFC PATCH v1 0/6] Fair scheduling Volodymyr Babchuk
2020-06-12 0:22 ` [RFC PATCH v1 2/6] sched: track time spent in hypervisor tasks Volodymyr Babchuk
2020-06-12 4:43 ` Jürgen Groß
2020-06-12 11:30 ` Volodymyr Babchuk
2020-06-12 11:40 ` Jürgen Groß
2020-09-24 18:08 ` Volodymyr Babchuk
2020-09-25 17:22 ` Dario Faggioli
2020-09-25 20:21 ` Volodymyr Babchuk
2020-09-25 21:42 ` Dario Faggioli
2020-06-16 10:10 ` Jan Beulich
2020-06-18 2:50 ` Volodymyr Babchuk
2020-06-18 6:34 ` Jan Beulich
2020-06-12 0:22 ` [RFC PATCH v1 1/6] sched: track time spent in IRQ handler Volodymyr Babchuk
2020-06-12 4:36 ` Jürgen Groß
2020-06-12 11:26 ` Volodymyr Babchuk
2020-06-12 11:29 ` Julien Grall
2020-06-12 11:33 ` Volodymyr Babchuk
2020-06-12 12:21 ` Julien Grall
2020-06-12 20:08 ` Dario Faggioli
2020-06-12 22:25 ` Volodymyr Babchuk
2020-06-12 22:54 ` Julien Grall
2020-06-16 10:06 ` Jan Beulich
2020-06-12 0:22 ` [RFC PATCH v1 3/6] sched, credit2: improve scheduler fairness Volodymyr Babchuk
2020-06-12 4:51 ` Jürgen Groß
2020-06-12 11:38 ` Volodymyr Babchuk
2020-06-12 0:22 ` [RFC PATCH v1 5/6] tools: xentop: show time spent in IRQ and HYP states Volodymyr Babchuk
2020-06-12 0:22 ` [RFC PATCH v1 6/6] trace: add fair scheduling trace events Volodymyr Babchuk
2020-06-12 0:22 ` [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics Volodymyr Babchuk
2020-06-12 4:57 ` Jürgen Groß
2020-06-12 11:44 ` Volodymyr Babchuk
2020-06-12 12:45 ` Julien Grall
2020-06-12 22:16 ` Volodymyr Babchuk [this message]
2020-06-18 20:24 ` Volodymyr Babchuk
2020-06-18 20:34 ` Julien Grall
2020-06-18 23:35 ` Volodymyr Babchuk
2020-06-12 12:29 ` Julien Grall
2020-06-12 12:41 ` Jürgen Groß
2020-06-12 15:29 ` Dario Faggioli
2020-06-12 22:27 ` Volodymyr Babchuk
2020-06-13 6:22 ` Jürgen Groß
2020-06-18 2:58 ` Volodymyr Babchuk
2020-06-18 15:17 ` Julien Grall
2020-06-18 15:23 ` Jan Beulich
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