From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Glauber Costa <glommer@redhat.com>
Cc: kvm@vger.kernel.org, avi@redhat.com, zamsden@redhat.com,
mtosatti@redhat.com, riel@redhat.com, peterz@infradead.org,
mingo@elte.hu
Subject: Re: [RFC v2 4/7] change kernel accounting to include steal time
Date: Mon, 30 Aug 2010 10:30:04 -0700 [thread overview]
Message-ID: <4C7BEA9C.1060605@goop.org> (raw)
In-Reply-To: <1283184391-7785-8-git-send-email-glommer@redhat.com>
On 08/30/2010 09:06 AM, Glauber Costa wrote:
> This patch proposes a common steal time implementation. When no
> steal time is accounted, we just add a branch to the current
> accounting code, that shouldn't add much overhead.
How is stolen time logically any different from a CPU running slowly due
to HT or power management? Is it worth trying to handle them in the
same way? (I'm mostly picking on the "_from_hypervisor" part, since
that seems over-specific.)
Why not have a get_unstolen_time() function which just returns
sched_clock() in the normal case, but can return less?
> When we do want to register steal time, we proceed as following:
> - if we would account user or system time in this tick, and there is
> out-of-cpu time registered, we skip it altogether, and account steal
> time only.
> - if we would account user or system time in this tick, and we got the
> cpu for the whole slice, we proceed normaly.
> - if we are idle in this tick, we flush out-of-cpu time to give it the
> chance to update whatever last-measure internal variable it may have.
>
> This approach is simple, but proved to work well for my test scenarios.
> in a UP guest on UP host, with a cpu-hog in both guest and host shows
> ~ 50 % steal time. steal time is also accounted proportionally, if
> nice values are given to the host cpu-hog.
>
> A cpu-hog in the host with no load in the guest, produces 0 % steal time,
> with 100 % idle, as one would expect.
>
> Signed-off-by: Glauber Costa <glommer@redhat.com>
> ---
> include/linux/sched.h | 1 +
> kernel/sched.c | 29 +++++++++++++++++++++++++++++
> 2 files changed, 30 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 0478888..e571ddd 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -312,6 +312,7 @@ long io_schedule_timeout(long timeout);
> extern void cpu_init (void);
> extern void trap_init(void);
> extern void update_process_times(int user);
> +extern cputime_t (*hypervisor_steal_time)(void);
> extern void scheduler_tick(void);
>
> extern void sched_show_task(struct task_struct *p);
> diff --git a/kernel/sched.c b/kernel/sched.c
> index f52a880..9695c92 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -3157,6 +3157,16 @@ unsigned long long thread_group_sched_runtime(struct task_struct *p)
> return ns;
> }
>
> +cputime_t (*hypervisor_steal_time)(void) = NULL;
> +
> +static inline cputime_t get_steal_time_from_hypervisor(void)
> +{
> + if (!hypervisor_steal_time)
> + return 0;
> + return hypervisor_steal_time();
> +}
> +
> +
> /*
> * Account user cpu time to a process.
> * @p: the process that the cpu time gets accounted to
> @@ -3169,6 +3179,12 @@ void account_user_time(struct task_struct *p, cputime_t cputime,
> struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
> cputime64_t tmp;
>
> + tmp = get_steal_time_from_hypervisor();
> + if (tmp) {
> + account_steal_time(tmp);
> + return;
> + }
Is that all? Does the scheduler use account_steal_time() to adjust its
scheduling decisions, or is it just something that gets shown to users?
I thought just the latter.
But if all you're doing is calling account_steal_time(), why bother with
all this get_steal_time_from_hypervisor() stuff? The
hypervisor-specific code can just call account_steal_time() directly.
> +
> /* Add user time to process. */
> p->utime = cputime_add(p->utime, cputime);
> p->utimescaled = cputime_add(p->utimescaled, cputime_scaled);
> @@ -3234,6 +3250,12 @@ void account_system_time(struct task_struct *p, int hardirq_offset,
> return;
> }
>
> + tmp = get_steal_time_from_hypervisor();
> + if (tmp) {
> + account_steal_time(tmp);
> + return;
> + }
> +
> /* Add system time to process. */
> p->stime = cputime_add(p->stime, cputime);
> p->stimescaled = cputime_add(p->stimescaled, cputime_scaled);
> @@ -3276,6 +3298,13 @@ void account_idle_time(cputime_t cputime)
> cputime64_t cputime64 = cputime_to_cputime64(cputime);
> struct rq *rq = this_rq();
>
> + /*
> + * if we're idle, we don't account it as steal time, since we did
> + * not want to run anyway. We do call the steal function, however, to
> + * give the guest the chance to flush its internal buffers
> + */
> + get_steal_time_from_hypervisor();
Eh? This doesn't make much sense. What side-effects is
get_steal_time_from_hypervisor() expected to have? If there's some
hypervisor-specific implementation detail, why not wrap that up in a
specific function rather than overloading this one?
J
next prev parent reply other threads:[~2010-08-30 17:30 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-08-30 16:06 [RFC v2 0/7] kvm stael time implementation Glauber Costa
2010-08-30 16:06 ` [RFC v2 1/7] change headers preparing for steal time Glauber Costa
2010-08-30 16:06 ` [RFC 1/8] Implement getnsboottime kernel API Glauber Costa
2010-08-30 16:06 ` [RFC v2 2/7] always call kvm_write_guest Glauber Costa
2010-08-30 16:06 ` [RFC 2/8] change headers preparing for steal time Glauber Costa
2010-08-30 16:06 ` [RFC 3/8] always call kvm_write_guest Glauber Costa
2010-08-30 16:06 ` [RFC v2 3/7] measure time out of guest Glauber Costa
2010-08-30 16:06 ` [RFC v2 4/7] change kernel accounting to include steal time Glauber Costa
2010-08-30 16:06 ` [RFC 4/8] measure time out of guest Glauber Costa
2010-08-30 16:06 ` [RFC 5/8] change kernel accounting to include steal time Glauber Costa
2010-08-30 16:06 ` [RFC v2 5/7] kvm steal time implementation Glauber Costa
2010-08-30 16:06 ` [RFC 6/8] " Glauber Costa
2010-08-30 16:06 ` [RFC v2 6/7] touch softlockup watchdog Glauber Costa
2010-08-30 16:06 ` [RFC v2 7/7] tell guest about steal time feature Glauber Costa
2010-08-30 16:06 ` [RFC 7/8] touch softlockup watchdog Glauber Costa
2010-08-30 16:06 ` [RFC 8/8] tell guest about steal time feature Glauber Costa
2010-08-30 17:33 ` [RFC v2 6/7] touch softlockup watchdog Jeremy Fitzhardinge
2010-08-30 18:07 ` Glauber Costa
2010-08-30 16:46 ` [RFC 5/8] change kernel accounting to include steal time Peter Zijlstra
2010-08-30 17:26 ` Glauber Costa
2010-08-30 17:30 ` Jeremy Fitzhardinge [this message]
2010-08-30 18:39 ` [RFC v2 4/7] " Rik van Riel
2010-08-30 19:07 ` Jeremy Fitzhardinge
2010-08-30 19:14 ` Peter Zijlstra
2010-08-30 19:17 ` Rik van Riel
2010-08-30 19:20 ` Peter Zijlstra
2010-08-30 19:45 ` Rik van Riel
2010-08-30 22:56 ` Jeremy Fitzhardinge
2010-08-30 23:03 ` Rik van Riel
2010-08-31 8:11 ` Peter Zijlstra
2010-09-02 18:19 ` Glauber Costa
2010-09-03 3:24 ` Jeremy Fitzhardinge
2010-09-03 7:18 ` Peter Zijlstra
2010-09-01 23:56 ` [RFC 1/8] Implement getnsboottime kernel API Zachary Amsden
2010-08-30 16:37 ` [RFC v2 0/7] kvm stael time implementation Peter Zijlstra
2010-08-30 16:45 ` Jeremy Fitzhardinge
2010-08-30 17:21 ` Glauber Costa
2010-08-30 17:20 ` Jeremy Fitzhardinge
2010-08-30 17:06 [RFC v2 0/7] kvm steal time implementation proposal Glauber Costa
2010-08-30 17:06 ` [RFC v2 4/7] change kernel accounting to include steal time Glauber Costa
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4C7BEA9C.1060605@goop.org \
--to=jeremy@goop.org \
--cc=avi@redhat.com \
--cc=glommer@redhat.com \
--cc=kvm@vger.kernel.org \
--cc=mingo@elte.hu \
--cc=mtosatti@redhat.com \
--cc=peterz@infradead.org \
--cc=riel@redhat.com \
--cc=zamsden@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).