[I haven't read the diff, just a short comment]
Dipankar Sarma wrote:
rcu_state came over from Manfred's RCU_HUGE patch IIRC. I don't
think it is necessary to allocate rcu_state separately in the
current mainline RCU code. So, the patch looks OK to me, but
Manfred might see something that I am not seeing.
The two-level rcu code was never merged, I still plan to clean it up.
But the idea of splitting the control block and the state is used in the
current code:
- __rcu_pending() is the hot path, it only performs a read access to
rcu_ctrlblk.
- write accesses to the rcu_ctrlblk are really rare, they only happen
when a new batch is started. Especially: independant from the number of
cpus.
Write access to the rcu_state are common:
- each cpu must write once in each cycle to update it's cpu mask.
- The last cpu then completes the quiescent cycle.
The idea is that rcu_state is more or less write-only and rcu_state is
read-only. Theoretically, rcu_state could be shared in all cpus caches,
and there will be only one invalidate when a new batch is started. Thus
no cacheline trashing due to rcu_pending calls.
I think it would be safer to keep the two state counters in a separate
cacheline from the spinlock and the cpu mask, but I don't have any hard
numbers. IIRC the problems with the large SGI systems disappered, and
everyone was happy. No real benchmark comparisons were made.
--
Manfred
-
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]
