From mboxrd@z Thu Jan 1 00:00:00 1970 From: Eric Piel Date: Fri, 14 Mar 2003 14:34:36 +0000 Subject: [Linux-ia64] Re: [BUG] nanosleep() granularity bumps up in 2.5.64 (was: [PATCH] Message-Id: List-Id: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org David Mosberger wrote: > Are you running ntp? Yes (I hadn't noticed it) but it was not connected to any server and disabling it doesn't change the results. > > On 2.5: > > $ time sleep 16 > real 0m16.002s > user 0m0.001s > sys 0m0.002s > > $ time sleep 16.02 > real 0m25.189s > user 0m0.000s > sys 0m0.001s > > So clearly something very strange is going on. My suspicion is that > the bug was introduced back when x86 switched from 100Hz to 1000Hz > ticks, but that's just a guess. Eric, would you be > able/willing/interested to look into this? Sure, I aim at porting the high resolution timers but any annoying bug related to the time can be interesting to remove. Coincidently Vita has just reported a bug on the lkml which, after a closer look, seems to be the same: > When playing with select() timeout values I found that granularity > of nanosleep() in 2.5.64 kernel bumps to 256 msec. Trying to get finer > granularity it ends up sleeping to the next multiple of 256 msec >From what I understand their is a bug in the timers that causes a big granularity. The case of Vita is a very good example. Also, after 16s it seems the granuality (slowly?!) jumps from 1/64th s to 16s! : sleep requested time obtained 14.000000000 14.006201744 15.000000000 15.006647110 16.000000000 16.007089615 17.000000000 18.742679596 18.000000000 32.014190674 19.000000000 32.014190674 20.000000000 32.014190674 I think lines like that from patch-2.5.64 are very suspicious to be related to the bug: + base->timer_jiffies = INITIAL_JIFFIES; + base->tv1.index = INITIAL_JIFFIES & TVR_MASK; + base->tv2.index = (INITIAL_JIFFIES >> TVR_BITS) & TVN_MASK; + base->tv3.index = (INITIAL_JIFFIES >> (TVR_BITS+TVN_BITS)) & TVN_MASK; + base->tv4.index = (INITIAL_JIFFIES >> (TVR_BITS+2*TVN_BITS)) & TVN_MASK; + base->tv5.index = (INITIAL_JIFFIES >> (TVR_BITS+3*TVN_BITS)) & TVN_MASK; Any idea/sugestion/patch is welcomed. Whatever, I will try to fix this as soon as I'm back from my week end :-) Eric