Messages in this thread |  | | From | Nikita Danilov <> | Date | Fri, 21 Sep 2001 13:32:54 +0400 | Subject | Re: [reiserfs-list] Re: [PATCH] Significant performace improvements on reiserfs systems |
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Andrew Morton writes: > george anzinger wrote: > > > > ... > > Actually, I rather think that the problem is lock granularity. These > > issues are present in the SMP systems as well. A good solution would be > > one that shortened the spinlock time. No horrid preempt code, just > > tight fast code. > > > > This may not be practical. > > Take, for example, zap_page_range(). It simply has a lot > of work to do, and it does it inside a spinlock. By doing > it in a tight loop, it's optimal. > > There is no way to speed this function up by two or three orders > of magnitude. (Well, there is: don't take the lock at all if > the mm isn't shared, but this is merely an example. There are > other instances). > > It seems that for a preemptive kernel to be successful, we need > to globally alter the kernel so that it never holds locks for > more than 500 microseconds. Which is what the conditional_schedule() > (aka cooperative multitasking :)) patches do. > > It seems that there are no magic bullets, and low latency will > forever have a global impact on kernel design, unless a way is > found to reschedule with locks held. I recall that a large
In Solaris, before spinning on a busy spin-lock, thread checks whether spin-lock holder runs on the same processor. If so, thread goes to sleep and holder wakes it up on spin-lock release. The same, I guess is going for interrupts that are served as separate threads. This way, one can re-schedule with spin-locks held.
> part of the MontaVista patch involved turning spinlocks into > semaphores, yes? That would seem to be the way to go.
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