From: Viresh Kumar <viresh.kumar@linaro.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel
Date: Wed, 20 May 2015 19:34:11 +0530 [thread overview]
Message-ID: <20150520140411.GB22904@linux> (raw)
In-Reply-To: <alpine.DEB.2.11.1505201411500.4225@nanos>
On 20-05-15, 15:09, Thomas Gleixner wrote:
> On Wed, 20 May 2015, Viresh Kumar wrote:
> They look at clock_event_mode and not at state, right?
Yeah, it was all useful (that's what I thought initially, but not
anymore) only when we migrate some drivers to the new per-state APIs.
> And that way we add the overhead of a full function call to those
> drivers for the interrupt hot path?
Honestly, I didn't realize that this can be a blocker. My bad.
> Of course you should have done that analysis before posting some
> random helper functions.
I did looked at all the drivers few days back, but failed to give a
summary similar to yours. No excuses.
> Lets look how useful these functions are for the various use cases
>
> #1) Adds function call over head to the timer interrupt
>
> Hot path does matter and that function call is a regression. So
> that's a NONO
> Now explain me how your magic functions help. For most of the cases
> they would be a performance regression. And for the rest they really
> do not matter at all.
They wouldn't help at all in that case.
So, probably we are left with following choices:
- Maintain state internally within the driver. SMP cases need per-cpu
storage as clkevt devices are per-cpu. Probably that's a NONO as
well ?
- Use CLK_EVT_STATE_* directly in drivers (similar to the way we use
CLK_EVT_MODE_* today).
- Write the routines I proposed as macros or inline functions in
clockchips.h, and use them. Of course that wouldn't stop exposing
CLK_EVT_STATE_* to rest of the kernel.
- Something else ?
Which one do you suggest ?
--
viresh
next prev parent reply other threads:[~2015-05-20 14:04 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-20 9:06 [PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel Viresh Kumar
2015-05-20 9:06 ` [PATCH 1/2] clockevents: Move 'enum clock_event_state' to tick-internal.h Viresh Kumar
2015-05-20 9:06 ` [PATCH 2/2] clockevents: Add helpers to verify state of a clockevent device Viresh Kumar
2015-05-20 13:09 ` [PATCH 0/2] clockevents: Hide CLOCK_EVT_STATE_* from rest of the kernel Thomas Gleixner
2015-05-20 14:04 ` Viresh Kumar [this message]
2015-05-20 14:20 ` Thomas Gleixner
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