On Fri, Sep 23, 2011 at 7:39 AM, Marc Dietrich <marvin24@xxxxxx> wrote: > Hi, > > arch/arm/mach-tegra/cpu-tegra.c (as from nv-tegra.nvidia.com) contains a some > strange comment: > > 493 /* FIXME: what's the actual transition time? */ > 494 policy->cpuinfo.transition_latency = 300 * 1000; > > The trees on chromeos.org (both, kernel and kernel-next) have: > > 392 /* cpu clock change latency: ~400us */ > 393 policy->cpuinfo.transition_latency = 400; > > because according to > > http://git.chromium.org/gitweb/?p=chromiumos/third_party/kernel.git;a=commitdiff;h=6a4debe346f5946f4fab14b413885896b7cde324 > > this improves latency of the GUI. Note that the comment said "us", while the cpu > transition latency is measured in "ns", so 400 * 1000 would be right. > > So either the comment is wrong (should be 400ns) or the patch is wrong (which is > unlikely, because it improved latency in the testcase). > > Can someone comment on this? cpu-tegra.c says latency is 300 uS because relocking the CPU pll has a udelay(300). 400 nS would just make the ondemand governor sample more often than it means to. I doubt changing it to 400 uS makes any difference. > Thanks > > Marc > -- > To unsubscribe from this list: send the line "unsubscribe linux-tegra" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
