On 08/22/13 10:33, Santosh Shilimkar wrote: > On Thursday 22 August 2013 01:06 PM, Stephen Boyd wrote: >> On some ARM systems there are two sets of per-cpu timers: the TWD >> timers and the global timers. The TWD timers are rated at 350 and >> the global timers are rated at 300 but the TWD timers suffer from >> FEAT_C3_STOP while the arm global timers don't. The tick device >> selection logic doesn't consider the FEAT_C3_STOP flag so we'll >> always end up with the TWD as the tick device although we don't >> want that. >> >> Extend the preference logic to take the FEAT_C3_STOP flag into >> account and always prefer tick devices that don't suffer from >> FEAT_C3_STOP even if their rating is lower than tick devices that >> do suffer from FEAT_C3_STOP. This will remove the need to do any >> broadcasting on such ARM systems. >> >> Signed-off-by: Stephen Boyd <sb...@codeaurora.org> >> --- >> kernel/time/tick-common.c | 14 ++++++++++++-- >> 1 file changed, 12 insertions(+), 2 deletions(-) >> >> diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c >> index 64522ec..3ae437d 100644 >> --- a/kernel/time/tick-common.c >> +++ b/kernel/time/tick-common.c >> @@ -244,12 +244,22 @@ static bool tick_check_preferred(struct >> clock_event_device *curdev, >> return false; >> } >> >> + if (!curdev) >> + return true; >> + >> + /* Always prefer a tick device that doesn't suffer from FEAT_C3STOP */ >> + if (!(newdev->features & CLOCK_EVT_FEAT_C3STOP) && >> + (curdev->features & CLOCK_EVT_FEAT_C3STOP)) >> + return true; >> + if ((newdev->features & CLOCK_EVT_FEAT_C3STOP) && >> + !(curdev->features & CLOCK_EVT_FEAT_C3STOP)) >> + return false; >> + > I don't think preferring the clock-event which doesn't suffer > from FEAT_C3STOP is a good idea if the quality of the time source > is not same. Generally the global timers are slow and far away from > CPU(cycle cost). So as long as we don't get impacted because of low power > states, the tick should run out of local timers which are faster access > as well as high resolution. >
Fair enough. I have no data either way to convince anyone that this is a good or bad idea so this patch should have probably been an RFC. Are you hinting at something like switching to a per-cpu timer that doesn't suffer from FEAT_C3_STOP when a CPU goes into a deep idle state? Interesting idea but I think I'll leave that to someone else if they really care to do that. -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
