Re: too many timer retries happen when do local timer swtich with broadcast timer

Santosh Shilimkar
2013-02-22T10:06:39Z

Thomas,

On Friday 22 February 2013 03:49 AM, Thomas Gleixner wrote:
> On Thu, 21 Feb 2013, Santosh Shilimkar wrote:
>> On Thursday 21 February 2013 07:18 PM, Thomas Gleixner wrote:
>>> find below a completely untested patch, which should address that issue.
>>>
>> After looking at the thread, I tried to see the issue on OMAP and could
>> see the same issue as Jason.
>
> That's interesting. We have the same issue on x86 since 2007 and
> nobody noticed ever. It's basically the same problem there, but it
> seems that on x86 getting out of those low power states is way slower
> than the minimal reprogramming delta which is used to enforce the
> local timer to fire after the wakeup.
>
> I'm still amazed that as Jason stated a 1us reprogramming delta is
> sufficient to get this ping-pong going. I somehow doubt that, but
> maybe ARM is really that fast :)
>
>> Your patch fixes the retries on both CPUs on my dual core machine. So
>> you use my tested by if you need one.
>
> They are always welcome.
>
BTW, Lorenzo off-list mentioned to me about warning in boot-up
which I missed while testing your patch. It will take bit more
time for me to look into it and hence thought of reporting it.

[ 2.186126] ------------[ cut here ]------------
[ 2.190979] WARNING: at kernel/time/tick-broadcast.c:501
tick_broadcast_oneshot_control+0x1c0/0x21c()
[ 2.200622] Modules linked in:
[ 2.203826] [<c001bfe4>] (unwind_backtrace+0x0/0xf0) from
[<c0047d6c>] (warn_slowpath_common+0x4c/0x64)
[ 2.213653] [<c0047d6c>] (warn_slowpath_common+0x4c/0x64) from
[<c0047da0>] (warn_slowpath_null+0x1c/0x24)
[ 2.223754] [<c0047da0>] (warn_slowpath_null+0x1c/0x24) from
[<c009336c>] (tick_broadcast_oneshot_control+0x1c0/0x21c)
[ 2.234924] [<c009336c>] (tick_broadcast_oneshot_control+0x1c0/0x21c)
from [<c00928dc>] (tick_notify+0x23c/0x42c)
[ 2.245666] [<c00928dc>] (tick_notify+0x23c/0x42c) from [<c0539a3c>]
(notifier_call_chain+0x44/0x84)
[ 2.255218] [<c0539a3c>] (notifier_call_chain+0x44/0x84) from
[<c0071068>] (raw_notifier_call_chain+0x18/0x20)
[ 2.265686] [<c0071068>] (raw_notifier_call_chain+0x18/0x20) from
[<c0091c70>] (clockevents_notify+0x2c/0x174)
[ 2.276123] [<c0091c70>] (clockevents_notify+0x2c/0x174) from
[<c0035294>] (omap_enter_idle_smp+0x3c/0x120)
[ 2.286315] [<c0035294>] (omap_enter_idle_smp+0x3c/0x120) from
[<c042e504>] (cpuidle_enter+0x14/0x18)
[ 2.295928] [<c042e504>] (cpuidle_enter+0x14/0x18) from [<c042ef14>]
(cpuidle_wrap_enter+0x34/0xa0)
[ 2.305389] [<c042ef14>] (cpuidle_wrap_enter+0x34/0xa0) from
[<c042eb20>] (cpuidle_idle_call+0xe0/0x328)
[ 2.315307] [<c042eb20>] (cpuidle_idle_call+0xe0/0x328) from
[<c0015100>] (cpu_idle+0x8c/0x11c)
[ 2.324401] [<c0015100>] (cpu_idle+0x8c/0x11c) from [<c073d7ac>]
(start_kernel+0x2b0/0x300)
[ 2.333129] ---[ end trace 6fe1f7b4606a9e20 ]---