From: Julien Grall <julien@xen.org>
To: "Jürgen Groß" <jgross@suse.com>,
"Volodymyr Babchuk" <Volodymyr_Babchuk@epam.com>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Dario Faggioli <dfaggioli@suse.com>,
Jan Beulich <jbeulich@suse.com>
Subject: Re: [RFC PATCH v1 4/6] xentop: collect IRQ and HYP time statistics.
Date: Fri, 12 Jun 2020 13:29:56 +0100 [thread overview]
Message-ID: <88eac035-8769-24f7-45e6-11a1c4739ccb@xen.org> (raw)
In-Reply-To: <2a0ff6f5-1ada-9d0a-5014-709c873ec3e3@suse.com>
Hi Juergen,
On 12/06/2020 05:57, 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.
add_sized() is definitely not atomic. It will only prevent the compiler
to read/write multiple time the variable.
If we expect sched_get_time_correction to be called concurrently then we
would need to introduce atomic64_t or a spin lock.
Cheers,
--
Julien Grall
next prev parent reply other threads:[~2020-06-12 12:30 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
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 [this message]
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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