Messages in this thread | | | Date | Fri, 5 Mar 2004 21:44:34 +0000 | From | Jamie Lokier <> | Subject | Re: 2.4.23aa2 (bugfixes and important VM improvements for the high end) |
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Andrea Arcangeli wrote: > > Can you use a read-write lock, so that userspace copies only need to > > take the lock for reading? That doesn't eliminate cacheline bouncing > > but does eliminate the serialisation. > > normally the bouncing would be the only overhead, but here I also think > the serialization is a significant factor of the contention because the > critical section is taking lots of time. So I would expect some > improvement by using a read/write lock.
For something as significant as user<->kernel data transfers, it might be worth eliminating the bouncing as well - by using per-CPU * per-mm spinlocks.
User<->kernel data transfers would take the appropriate per-CPU lock for the current mm, and not take page_table_lock. Everything that normally takes page_table_lock would, and also take all of the per-CPU locks.
That does require a set of per-CPU spinlocks to be allocated whenever a new mm is allocated (although the sets could be cached so it needn't be slow).
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