Messages in this thread | | | From | John Ogness <> | Subject | Re: [PATCH printk] printk: flush consoles before checking progress | Date | Wed, 04 Oct 2023 12:31:07 +0206 |
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On 2023-10-02, Petr Mladek <pmladek@suse.com> wrote: > I was about to push this patch and ran checkpatch.pl. It warned about > > WARNING: msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.rst > #73: FILE: kernel/printk/printk.c:3782: > + msleep(1); > > And indeed, Documentation/timers/timers-howto.rst says that msleep() > might sleep longer that expected for <20ms delays. I guess that > it is somehow related to jiffies, HZ, and load on the system. > > I think that we need to count jiffies here.
Agreed. The @timeout_ms parameter should be respected.
> Something like: > > diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c > index db81b68d7f14..6ea500d95fd9 100644 > --- a/kernel/printk/printk.c > +++ b/kernel/printk/printk.c > @@ -3723,7 +3723,8 @@ late_initcall(printk_late_init); > /* If @con is specified, only wait for that console. Otherwise wait for all. */ > static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progress) > { > - int remaining = timeout_ms; > + unsigned long timeout_jiffies = msecs_to_jiffies(timeout_ms); > + unsigned_long timeout_end = jiffies + timeout_jiffies; > struct console *c; > u64 last_diff = 0; > u64 printk_seq; > @@ -3772,24 +3773,19 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre > console_srcu_read_unlock(cookie); > > if (diff != last_diff && reset_on_progress) > - remaining = timeout_ms; > + timeout_end = jiffies + timeout_jiffies; > > console_unlock(); > > /* Note: @diff is 0 if there are no usable consoles. */ > - if (diff == 0 || remaining == 0) > + if (diff == 0) > break; > > - if (remaining < 0) { > - /* no timeout limit */ > - msleep(100); > - } else if (remaining < 100) { > - msleep(remaining); > - remaining = 0; > - } else { > - msleep(100); > - remaining -= 100; > - } > + /* Negative timeout means an infinite wait. */ > + if (timeout_ms >= 0 && time_after_eq(jiffies, timeout_end)) > + break; > + > + msleep(2000 / HZ);
Is there really any advantage to this? I would just do msleep(1) and let msleep round up. Everything else (tracking via jiffies) looks fine to me.
> last_diff = diff; > } > > And we should do this in a separate patch. It seems that sleeping > is a bigger magic than I expected.
Agreed.
John
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