From: Thomas Gleixner <tglx@linutronix.de>
To: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
Richard Cochran <richardcochran@gmail.com>,
Ingo Molnar <mingo@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
Prarit Bhargava <prarit@redhat.com>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Jan Kara <jack@suse.cz>, Jiri Bohac <jbohac@suse.cz>,
Ingo Molnar <mingo@redhat.com>,
Shuah Khan <shuahkh@osg.samsung.com>
Subject: Re: [RFC][PATCH 4/4] time: Do leapsecond adjustment in gettime fastpaths
Date: Mon, 8 Jun 2015 22:02:18 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.11.1506082151410.4133@nanos> (raw)
In-Reply-To: <alpine.DEB.2.11.1506082030090.4133@nanos>
On Mon, 8 Jun 2015, Thomas Gleixner wrote:
> On Mon, 8 Jun 2015, John Stultz wrote:
> > Now, It could be possible to do a lighter weight version of my patch,
> > which just does the adjustment only for the hrtimer_interrupt code
> > (leaving the rest of the read paths alone).
>
> Yes, that should work. As long as I can keep the cached values in the
> hrtimer cpu bases and the whole thing keeps the clock_was_set_seq
> logic intact.
>
> If we do not do the conditional version, then on every hrtimer
> interrupt we write THREE cachelines for nothing.
>
> And if we cannot cache the offsets, then we end up calling into the
> timekeeping code for every timer which is not CLOCK_MONOTONIC based
> and retrieve the offset. That hurts especially on 32bit machines,
> because we need to protect the readout with the timekeeper sequence
> counter.
Below is a patch which just has the required data in the right place
and the changes to ktime_get_update_offsets_now().
It's simpler than your version as:
- there is no requirement to do the add in the first place as we
know the monotonic time at which the leap second happens.
- we can precalculate the leap adjusted offset and just replace
the non adjusted offset for the window.
When the whole thing is over you just need to increment the
clock_was_set_seq counter so the next timer interrupt will cache the
normal values again.
Thanks,
tglx
diff --git a/include/linux/timekeeper_internal.h b/include/linux/timekeeper_internal.h
index e1f5a1136554..ecd193c23676 100644
--- a/include/linux/timekeeper_internal.h
+++ b/include/linux/timekeeper_internal.h
@@ -90,6 +90,9 @@ struct timekeeper {
ktime_t offs_tai;
s32 tai_offset;
unsigned int clock_was_set_seq;
+ ktime_t next_leap_ktime;
+ ktime_t offs_real_leap_adjusted;
+
struct timespec64 raw_time;
/* The following members are for timekeeping internal use */
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index 90ed5db67c1d..0de85bf9e331 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -1952,15 +1952,21 @@ ktime_t ktime_get_update_offsets_now(unsigned int *cwsseq, ktime_t *offs_real,
base = tk->tkr_mono.base;
nsecs = timekeeping_get_ns(&tk->tkr_mono);
+ base = ktime_add_ns(base, nsecs);
+
if (*cwsseq != tk->clock_was_set_seq) {
*cwsseq = tk->clock_was_set_seq;
*offs_real = tk->offs_real;
*offs_boot = tk->offs_boot;
*offs_tai = tk->offs_tai;
}
+
+ if (base.tv64 >= tk->next_leap_ktime.tv64)
+ *offs_real = tk->offs_real_leap_adjusted;
+
} while (read_seqcount_retry(&tk_core.seq, seq));
- return ktime_add_ns(base, nsecs);
+ return base;
}
/**
next prev parent reply other threads:[~2015-06-08 20:02 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-29 20:24 [RFC][PATCH 0/4] Fixes for leapsecond expiring early ABS_TIME CLOCK_REALTIME timers John Stultz
2015-05-29 20:24 ` [RFC][PATCH 1/4] selftests: timers: Add leap-second timer edge testing to leap-a-day.c John Stultz
2015-05-29 20:24 ` [RFC][PATCH 2/4] timer_list: Add the base offset so remaining nsecs are accurate for non monotonic timers John Stultz
2015-05-29 20:24 ` [RFC][PATCH 3/4] ntp: Use printk_deferred in leapsecond path John Stultz
2015-06-02 10:31 ` Jiri Bohac
2015-06-02 10:43 ` Jiri Kosina
2015-06-02 16:14 ` John Stultz
2015-06-02 16:04 ` John Stultz
2015-05-29 20:24 ` [RFC][PATCH 4/4] time: Do leapsecond adjustment in gettime fastpaths John Stultz
2015-05-31 16:05 ` Richard Cochran
2015-06-02 9:01 ` Ingo Molnar
2015-06-02 9:21 ` Peter Zijlstra
2015-06-02 14:09 ` John Stultz
2015-06-02 15:52 ` John Stultz
2015-06-03 9:04 ` Ingo Molnar
2015-06-03 17:44 ` John Stultz
2015-06-04 6:48 ` Ingo Molnar
2015-06-05 0:08 ` John Stultz
2015-06-05 7:29 ` Peter Zijlstra
2015-06-05 9:04 ` Richard Cochran
2015-06-05 9:10 ` Peter Zijlstra
2015-06-05 14:12 ` Richard Cochran
2015-06-05 17:28 ` John Stultz
2015-06-06 9:44 ` Thomas Gleixner
2015-06-08 17:55 ` John Stultz
2015-06-08 19:05 ` Thomas Gleixner
2015-06-08 20:02 ` Thomas Gleixner [this message]
2015-06-05 11:37 ` Prarit Bhargava
2015-06-05 12:07 ` Thomas Gleixner
2015-06-05 14:22 ` Richard Cochran
2015-06-05 17:24 ` John Stultz
2015-05-31 13:55 ` [RFC][PATCH 0/4] Fixes for leapsecond expiring early ABS_TIME CLOCK_REALTIME timers Prarit Bhargava
2015-06-01 11:57 ` Prarit Bhargava
2015-06-01 17:02 ` John Stultz
2015-06-01 17:43 ` Prarit Bhargava
2015-06-01 20:18 ` Daniel Bristot de Oliveira
2015-06-01 20:32 ` John Stultz
2015-06-01 21:42 ` Prarit Bhargava
2015-06-01 22:29 ` Daniel Bristot de Oliveira
2015-06-02 6:19 ` John Stultz
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