On 07/30/2015 10:16 PM, Waiman Long wrote:
On 07/29/2015 06:21 PM, Eric W. Biederman wrote:
Two quick questions.
- What motivates this work? Are you seeing lots of
parallel reads on proc?
The micro-benchmark that I used was artificial, but it was used to
reproduce an exit hanging problem that I saw in real application. In
fact, only allow one task to do a lookup seems too limiting to me.
- Why not rcu? Additions and removal of proc generic
files is very rare. Conversion to rcu for reads should
perform better and not take much more work.
RCU is harder to verify its correctness, whereas rwlock is easier to
use and understand. If it is really a performance critical path where
every extra bit of performance counts, I will certainly think RCU may
be the right choice. However, in this particular case, I don't think
using RCU will give any noticeable performance gain compared with a
rwlock.
One more thing, RCU is typically used with linked list. It is not easy
to use RCU with rbtree and may require major changes to the code.
Another alternative is to use seqlock + RCU, but it will still need more
code changes than rwlock.
Cheers,
Longman
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