Messages in this thread | | | From | Mitchel Humpherys <> | Subject | Re: [PATCH RESEND v8] iopoll: Introduce memory-mapped IO polling macros | Date | Mon, 24 Nov 2014 17:21:09 -0800 |
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On Mon, Nov 24 2014 at 04:53:19 PM, "Elliott, Robert (Server Storage)" <Elliott@hp.com> wrote: >> -----Original Message----- >> From: linux-kernel-owner@vger.kernel.org [mailto:linux-kernel- >> owner@vger.kernel.org] On Behalf Of Mitchel Humpherys >> Sent: Monday, 24 November, 2014 2:15 PM > ... >> From: Matt Wagantall <mattw@codeaurora.org> >> >> It is sometimes necessary to poll a memory-mapped register until its value >> satisfies some condition. Introduce a family of convenience macros that do >> this. Tight-looping, sleeping, and timing out can all be accomplished >> using these macros. >> > ... >> +#define readx_poll_timeout(op, addr, val, cond, sleep_us, timeout_us) \ >> +({ \ >> + ktime_t timeout = ktime_add_us(ktime_get(), timeout_us); \ >> + might_sleep_if(sleep_us); \ >> + for (;;) { \ >> + (val) = op(addr); \ >> + if (cond) \ >> + break; \ >> + if (timeout_us && ktime_compare(ktime_get(), timeout) > 0) { >> \ >> + (val) = op(addr); \ >> + break; \ >> + } \ >> + if (sleep_us) \ >> + usleep_range((sleep_us >> 2) + 1, sleep_us); \ > > The hpsa SCSI driver used to use usleep_range in a loop like > that, but we found that it caused scheduler problems during > boots because it uses TASK_UNINTERRUPTIBLE: > [ 9.260668] [sched_delayed] sched: RT throttling activated > > msleep() worked much better.
Hmm, maybe you were just sleeping for too long? According to Documentation/timers/timers-howto.txt, usleep_range is what should be used for non-atomic sleeps in the range [10us, 20ms]. Plus we need microsecond granularity anyways, so msleep wouldn't cut it.
If there are any potential users of these macros that would want to sleep for more than 20ms I guess we could add a special case here to use msleep when sleep_us exceeds 20,000 or so.
-Mitch
-- Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project
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