Messages in this thread | | | Date | Fri, 17 Dec 2004 12:10:08 -0800 | From | Nish Aravamudan <> | Subject | Re: dynamic-hz |
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On Mon, 13 Dec 2004 20:29:39 -0800, Andrew Morton <akpm@osdl.org> wrote: > Nish Aravamudan <nish.aravamudan@gmail.com> wrote: > > > > On Mon, 13 Dec 2004 03:25:21 -0800, Andrew Morton <akpm@osdl.org> wrote: > > > Andrea Arcangeli <andrea@suse.de> wrote: > > > > > > > > The patch only does HZ at dynamic time. But of course it's absolutely > > > > trivial to define it at compile time, it's probably a 3 liner on top of > > > > my current patch ;). However personally I don't think the three liner > > > > will worth the few seconds more spent configuring the kernel ;). > > > > > > We still have 1000-odd places which do things like > > > > > > schedule_timeout(HZ/10); > > > > Yes, yes, we do :) I replaced far more than I ever thought I could... > > There are a few issues I have with the remaining schedule_timeout() > > calls which I think fit ok with this thread... I'd especially like > > your input, Andrew, as you end up getting most of my patches from KJ. > > > > Many drivers use > > > > set_current_state(TASK_{UN,}INTERRUPTIBLE); > > schedule_timeout(1); // or some other small value < 10 > > > > This may or may not hide a dependency on a particular HZ value. If the > > code is somewhat old, perhaps the author intended the task to sleep > > for 1 jiffy when HZ was equal to 100. That meants that they ended up > > sleeping for 10 ms. If the code is new, the author intends that the > > task sleeps for 1 ms (HZ==1000). The question is, what should the > > replacement be? > > Presumably they meant 10 milliseconds. Or at least, that is the delay > which the developer did his testing with. > > > If they really meant to use schedule_timeout(1) in the sense of > > highest resolution delay possible (the latter above), then they > > probably should just call schedule() directly. > > argh. Never do that. It's basically a busywait and can cause lockups if > the calling task has realtime scheduling policy.
For those drivers that use schedule() calls currently to delay, what would you recommend? drivers/atm/ambassador.c contains a few examples. I can get rid of most of the schedule_timeout() calls, but the schedule() ones are a little more difficult. Would schedule_timeout(1) be preferred to schedule()?
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