On 2019/7/26 下午8:53, Jason Wang wrote:
On 2019/7/26 下午8:38, Michael S. Tsirkin wrote:
On Fri, Jul 26, 2019 at 08:00:58PM +0800, Jason Wang wrote:
On 2019/7/26 下午7:49, Michael S. Tsirkin wrote:
On Thu, Jul 25, 2019 at 10:25:25PM +0800, Jason Wang wrote:
On 2019/7/25 下午9:26, Michael S. Tsirkin wrote:
Exactly, and that's the reason actually I use synchronize_rcu()
there.
So the concern is still the possible synchronize_expedited()?
I think synchronize_srcu_expedited.
synchronize_expedited sends lots of IPI and is bad for realtime VMs.
Can I do this
on through another series on top of the incoming V2?
Thanks
The question is this: is this still a gain if we switch to the
more expensive srcu? If yes then we can keep the feature on,
I think we only care about the cost on srcu_read_lock() which
looks pretty
tiny form my point of view. Which is basically a READ_ONCE() +
WRITE_ONCE().
Of course I can benchmark to see the difference.
if not we'll put it off until next release and think
of better solutions. rcu->srcu is just a find and replace,
don't see why we need to defer that. can be a separate patch
for sure, but we need to know how well it works.
I think I get here, let me try to do that in V2 and let's see the
numbers.
Thanks
It looks to me for tree rcu, its srcu_read_lock() have a mb() which
is too
expensive for us.
I will try to ponder using vq lock in some way.
Maybe with trylock somehow ...
Ok, let me retry if necessary (but I do remember I end up with
deadlocks last try).
Ok, I play a little with this. And it works so far. Will do more testing
tomorrow.
One reason could be I switch to use get_user_pages_fast() to
__get_user_pages_fast() which doesn't need mmap_sem.
Thanks
