On Mon, 19 Jun 2006 10:12:52 +0200
Ingo Molnar <[email protected]> wrote:
>
> * Andrew Morton <[email protected]> wrote:
>
> > On Mon, 19 Jun 2006 09:02:29 +0200
> > Ingo Molnar <[email protected]> wrote:
> >
> > > Subject: increase spinlock-debug looping timeouts from 1 sec to 1
> > > min
> >
> > But it's broken. In the non-debug case we subtract RW_LOCK_BIAS so we
> > know that the writer will get the lock when all readers vacate. But
> > in the CONFIG_DEBUG_SPINLOCK case we don't do that, with the result
> > that taking a write_lock can take over a second.
> >
> > A much, much better fix (which involves visiting all architectures)
> > would be to subtract RW_LOCK_BIAS and _then_ wait for a second.
>
> no. Write-locks are unfair too, and there's no guarantee that writes are
> listened to. That's why nested read_lock() is valid, while nested
> down_read() is invalid.
>
> Take a look at arch/i386/kernel/semaphore.c, __write_lock_failed() just
> adds back the RW_LOCK_BIAS and retries in a loop. There's no difference
> to an open-coded write_trylock loop - unless i'm missing something
> fundamental.
OK. That sucks. A sufficiently large machine with the right mix of
latencies will get hit by the NMI watchdog in write_lock_irq().
But presumably the situation is much worse with CONFIG_DEBUG_SPINLOCK
because of that __delay().
So how about we remove the __delay() (which is wrong anyway, because
loops_per_jiffy isn't calculated with a write_trylock() in the loop (which
means we're getting scarily close to the NMI watchdog at present)).
Instead, calculate a custom loops_per_jiffy for this purpose in
lib/spinlock_debug.c?
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
