From: Marc Gonzalez <marc.w.gonzalez@free.fr> To: Arnd Bergmann <arnd@arndb.de> Cc: Will Deacon <will.deacon@arm.com>, Linux ARM <linux-arm-kernel@lists.infradead.org>, LKML <linux-kernel@vger.kernel.org>, Thierry Reding <thierry.reding@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Bjorn Andersson <bjorn.andersson@linaro.org>, Thomas Gleixner <tglx@linutronix.de>, Bjorn Helgaas <helgaas@kernel.org>, Douglas Anderson <dianders@chromium.org> Subject: Re: [PATCH v1] iopoll: Tweak readx_poll_timeout sleep range Date: Thu, 13 Jun 2019 18:04:41 +0200 [thread overview] Message-ID: <a732f522-5e65-3ac4-de04-802ef5455747@free.fr> (raw) In-Reply-To: <CAK8P3a1_WvHYW243MR5-NdFm3cSt+cVGM5EJmOM8uiQMQ3vQjQ@mail.gmail.com> On 13/06/2019 14:42, Arnd Bergmann wrote: > On Thu, Jun 13, 2019 at 2:16 PM Marc Gonzalez wrote: > >> Chopping max delay in 4 seems excessive. Let's just cut it in half. >> >> Signed-off-by: Marc Gonzalez <marc.w.gonzalez@free.fr> >> --- >> When max_us=100, old_min was 26 us; new_min would be 50 us >> Was there a good reason for the 1/4th? >> Is new_min=0 a problem? (for max=1) > > You normally want a large enough range between min and max. I don't > see anything wrong with a factor of four. Hmmm, I expect the typical use-case to be: "HW manual states operation X completes in 100 µs. Let's call usleep_range(100, foo); before hitting the reg." And foo needs to be a "reasonable" value: big enough to be able to merge several requests, low enough not to wait too long after the HW is ready. In this case, I'd say usleep_range(100, 200); makes sense. Come to think of it, I'm not sure min=26 (or min=50) makes sense... Why wait *less* than what the user specified? >> @@ -47,7 +47,7 @@ >> break; \ >> } \ >> if (__sleep_us) \ >> - usleep_range((__sleep_us >> 2) + 1, __sleep_us); \ >> + usleep_range(__sleep_us / 2, __sleep_us); \ >> } \ > > You are also missing the '+1' now, so this breaks with __sleep_us=1. It was on purpose. usleep_range(0, 1); is not well-defined? (I tried looking at the source, got lost down the rabbit hole.) Regards.
WARNING: multiple messages have this Message-ID (diff)
From: Marc Gonzalez <marc.w.gonzalez@free.fr> To: Arnd Bergmann <arnd@arndb.de> Cc: Douglas Anderson <dianders@chromium.org>, Will Deacon <will.deacon@arm.com>, LKML <linux-kernel@vger.kernel.org>, Bjorn Andersson <bjorn.andersson@linaro.org>, Thierry Reding <thierry.reding@gmail.com>, Bjorn Helgaas <helgaas@kernel.org>, Andrew Morton <akpm@linux-foundation.org>, Thomas Gleixner <tglx@linutronix.de>, Linux ARM <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH v1] iopoll: Tweak readx_poll_timeout sleep range Date: Thu, 13 Jun 2019 18:04:41 +0200 [thread overview] Message-ID: <a732f522-5e65-3ac4-de04-802ef5455747@free.fr> (raw) In-Reply-To: <CAK8P3a1_WvHYW243MR5-NdFm3cSt+cVGM5EJmOM8uiQMQ3vQjQ@mail.gmail.com> On 13/06/2019 14:42, Arnd Bergmann wrote: > On Thu, Jun 13, 2019 at 2:16 PM Marc Gonzalez wrote: > >> Chopping max delay in 4 seems excessive. Let's just cut it in half. >> >> Signed-off-by: Marc Gonzalez <marc.w.gonzalez@free.fr> >> --- >> When max_us=100, old_min was 26 us; new_min would be 50 us >> Was there a good reason for the 1/4th? >> Is new_min=0 a problem? (for max=1) > > You normally want a large enough range between min and max. I don't > see anything wrong with a factor of four. Hmmm, I expect the typical use-case to be: "HW manual states operation X completes in 100 µs. Let's call usleep_range(100, foo); before hitting the reg." And foo needs to be a "reasonable" value: big enough to be able to merge several requests, low enough not to wait too long after the HW is ready. In this case, I'd say usleep_range(100, 200); makes sense. Come to think of it, I'm not sure min=26 (or min=50) makes sense... Why wait *less* than what the user specified? >> @@ -47,7 +47,7 @@ >> break; \ >> } \ >> if (__sleep_us) \ >> - usleep_range((__sleep_us >> 2) + 1, __sleep_us); \ >> + usleep_range(__sleep_us / 2, __sleep_us); \ >> } \ > > You are also missing the '+1' now, so this breaks with __sleep_us=1. It was on purpose. usleep_range(0, 1); is not well-defined? (I tried looking at the source, got lost down the rabbit hole.) Regards. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next prev parent reply other threads:[~2019-06-13 16:04 UTC|newest] Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-06-13 12:16 [PATCH v1] iopoll: Tweak readx_poll_timeout sleep range Marc Gonzalez 2019-06-13 12:16 ` Marc Gonzalez 2019-06-13 12:42 ` Arnd Bergmann 2019-06-13 12:42 ` Arnd Bergmann 2019-06-13 16:04 ` Marc Gonzalez [this message] 2019-06-13 16:04 ` Marc Gonzalez 2019-06-13 16:11 ` Doug Anderson 2019-06-13 16:11 ` Doug Anderson 2019-06-13 16:36 ` Marc Gonzalez 2019-06-13 16:36 ` Marc Gonzalez 2019-06-13 17:10 ` Doug Anderson 2019-06-13 17:10 ` Doug Anderson
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