| Message ID | 0dfbe2976aa108c53e08d3477ea90f6360c1f54c.1403584026.git.viresh.kumar@linaro.org |
|---|---|
| State | Accepted |
| Commit | 89abb5ad10ae8ac3405e635ac80815f781c8b8e9 |
| Headers | show |
On Tue, Jun 24, 2014 at 10:01:01AM +0530, Viresh Kumar wrote: > We don't need 'broadcast' to be set to 'zero or one', but to 'zero or non-zero' > and so the extra operation to convert it to 'zero or one' can be skipped. > > Also change type of 'broadcast' to unsigned int, i.e. type of > drv->states[*].flags. All true; but does it change anything? That is, does your compiler generate better code because of this? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 24 June 2014 13:33, Peter Zijlstra <peterz@infradead.org> wrote: > All true; but does it change anything? That is, does your compiler > generate better code because of this? Compilers are smart enough now a days and may not perform !! at all I believe.. And so this patch is more about code clarity .. I tried comparing results for ARM and got this with/without this patch .. $ size ../bexynos/kernel/sched/idle.o text data bss dec hex filename 690 30 0 720 2d0 ../bexynos/kernel/sched/idle.o Don't know if some architectures are using somewhat dumb compilers which might result in better code with this patch :) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On Tue, 2014-06-24 at 10:03 +0200, Peter Zijlstra wrote: > On Tue, Jun 24, 2014 at 10:01:01AM +0530, Viresh Kumar wrote: > > We don't need 'broadcast' to be set to 'zero or one', but to 'zero or non-zero' > > and so the extra operation to convert it to 'zero or one' can be skipped. > > > > Also change type of 'broadcast' to unsigned int, i.e. type of > > drv->states[*].flags. > > All true; but does it change anything? That is, does your compiler > generate better code because of this? x86_64 gcc-4.8.3 made 1 less instruction, a shift. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
On 24 June 2014 17:48, Mike Galbraith <umgwanakikbuti@gmail.com> wrote:
> x86_64 gcc-4.8.3 made 1 less instruction, a shift.
I thought about doing this test for x86 as well, and over-estimated
compilers intelligence. I must have done it :)
And finally this patch is worth more than I originally estimated :)
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diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index cf009fb..9f1608f 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -79,7 +79,7 @@ static void cpuidle_idle_call(void) struct cpuidle_device *dev = __this_cpu_read(cpuidle_devices); struct cpuidle_driver *drv = cpuidle_get_cpu_driver(dev); int next_state, entered_state; - bool broadcast; + unsigned int broadcast; /* * Check if the idle task must be rescheduled. If it is the @@ -135,7 +135,7 @@ use_default: goto exit_idle; } - broadcast = !!(drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP); + broadcast = drv->states[next_state].flags & CPUIDLE_FLAG_TIMER_STOP; /* * Tell the time framework to switch to a broadcast timer
We don't need 'broadcast' to be set to 'zero or one', but to 'zero or non-zero' and so the extra operation to convert it to 'zero or one' can be skipped. Also change type of 'broadcast' to unsigned int, i.e. type of drv->states[*].flags. Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> --- Rebased over: 3.16-rc2. kernel/sched/idle.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)