From mboxrd@z Thu Jan 1 00:00:00 1970 From: linus.walleij@stericsson.com (Linus Walleij) Date: Thu, 11 Nov 2010 11:31:43 +0100 Subject: [PATCH] RFC: nomadik: expand timesource to 63 bits In-Reply-To: References: <1289466356-16697-1-git-send-email-linus.walleij@stericsson.com> Message-ID: <4CDBC60F.8070905@stericsson.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Thomas Gleixner wrote: > There is only one caveat. When nohz is on and you sleep longer than 16 > seconds then the limitation we have in place does not work anymore, as > it would say that the long sleep time is less than the 63bit > wraparound time. With 32bit clocksource it limits the sleep correclty > to avoid the clocksource wrap issue. Hm! So the .mask has that side effect (as I suspected), and with this the sleep will be limited to what time you can get into 63 bits (2200 years). And we sure want NOHZ... But if I complement the solution with the keepwarm() timer from Orion doing just a dummy read() on the clocksource every say 15 secs it will work even if the system sleeps for so long. > Aside of that you are trading a bit less source code with extra code > in the clock read() function, which is called pretty frequently. Hm, yeah. I would have to go to metrics but it's O(n) is it not? Shouldn't hurt a high-frequency SMP system I believe. Yours, Linus Walleij