Re: [PATCH] OsdSynch.c modernization

2007/9/22, Jung-uk Kim <jkim_at_freebsd.org>:
> I thought exactly the same when I started rewriting it (almost half
> year ago!).  I have tried all of the above, spent numerous sleepless
> nights, and miserably failed. :-(
>
> Spin mutex is too restrictive (e.g., it cannot be used with other
> locks gracefully).  critical_enter() causes:
>
> panic: blockable sleep lock (sleep mutex) 32 _at_
> /usr/src/sys/vm/uma_core.c:1830 cpuid = 0
> KDB: enter: panic
> [thread pid 21 tid 100013 ]
> Stopped at      kdb_enter+0x32: leave

UMA uses its own internal locking scheme which includes blocking
mutexes so you cannot maintain a spinlock over its functions.
You can however use a blocking mutex instead than a sx lock, that with
the help of adaptive spinning emulates a lot better spinlocks
behaviour.

Attilio


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