On 8/22/05, Peter T. Breuer <[EMAIL PROTECTED]> wrote: > "Also sprach Nish Aravamudan:" > > On 8/19/05, Alan Cox <[EMAIL PROTECTED]> wrote: > > > On Gwe, 2005-08-19 at 10:13 +0200, Peter T. Breuer wrote: > > > > The following "sleep under spinlock" is still present as of linux > > > > 2.6.12.5 in sound/oss/sequencer.c in midi_outc: > > > > > > > > > > > > n = 3 * HZ; /* Timeout */ > > > > > > > > spin_lock_irqsave(&lock,flags); > > > > while (n && !midi_devs[dev]->outputc(dev, data)) { > > > > interruptible_sleep_on_timeout(&seq_sleeper, HZ/25); > > > > n--; > > > > } > > > > spin_unlock_irqrestore(&lock,flags); > > > > > > > > > > > > I haven't thought about it, just noted it. It's been there forever > > > > (some others in the sound architecture have been gradually disappearing > > > > as newer kernels come out). > > > > > > Yep thats a blind substition of lock_kernel in an old tree it seems. > > > Probably my fault. Should drop it before the sleep and take it straight > > > after. > > > > Also, the use of n makes no sense. Indicates total sleep for 3 > > Well spotted. > > > seconds, but actually sleep for 40 milliseconds 3*HZ times > > (potentially)? > > I presume it should be > > n -= HZ/25;
Well that's the problem; you're presuming that an (eventual) schedule_timeout(HZ/25) call would actually sleep for HZ/25 jiffies. More than likely, though, it may sleep a little longer. Generally, code that is trying to sleep up to a certain time from now should use time_after() or time_before(). > (and "n > 0", of course). > > > In any case, probably should be: > > > > timeout = jiffies + 3*HZ; > > > > spin_lock_irqsave(&lock, flags); > > while (time_before(jiffies, timeout) && !midi_devs[dev]->outputc(dev, > > data)) { > > spin_unlock_irqrestore(&lock, flags); > > interruptible_sleep_on_timeout(&seq_sleeper, msecs_to_jiffies(40)); > > Well, you'd know. Is there something there really not taken care of by > "HZ"? 1) Makes this code consistent with other users in the kernel (Although I have tried to reduce the number of users of the sleep_on() family). 2) If HZ eventually is allowed to take other values (e.g., 864 for x86), then HZ/25 leads to rounding issues. msecs_to_jiffies() takes care of those issues *and* makes it a little clear what you're doing, IMO. Thanks, Nish - 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/