On 03/11/2017 10:40 PM, Mel Gorman wrote:
On Thu, Nov 02, 2017 at 07:21:09PM +0200, Tariq Toukan wrote:
On 18/09/2017 12:16 PM, Tariq Toukan wrote:
On 15/09/2017 1:23 PM, Mel Gorman wrote:
On Thu, Sep 14, 2017 at 07:49:31PM +0300, Tariq Toukan wrote:
Insights: Major degradation between #1 and #2, not getting any
close to linerate! Degradation is fixed between #2 and #3. This is
because page allocator cannot stand the higher allocation rate. In
#2, we also see that the addition of rings (cores) reduces BW (!!),
as result of increasing congestion over shared resources.
Unfortunately, no surprises there.
Congestion in this case is very clear. When monitored in perf
top: 85.58% [kernel] [k] queued_spin_lock_slowpath
While it's not proven, the most likely candidate is the zone lock
and that should be confirmed using a call-graph profile. If so, then
the suggestion to tune to the size of the per-cpu allocator would
mitigate the problem.
Indeed, I tuned the per-cpu allocator and bottleneck is released.
Hi all,
After leaving this task for a while doing other tasks, I got back to it now
and see that the good behavior I observed earlier was not stable.
Recall: I work with a modified driver that allocates a page (4K) per packet
(MTU=1500), in order to simulate the stress on page-allocator in 200Gbps
NICs.
There is almost new in the data that hasn't been discussed before. The
suggestion to free on a remote per-cpu list would be expensive as it would
require per-cpu lists to have a lock for safe remote access.
That's right, but each such lock will be significantly less congested
than the buddy allocator lock. In the flow in subject two cores need to
synchronize (one allocates, one frees).
We also need to evaluate the cost of acquiring and releasing the lock in
the case of no congestion at all.
However,
I'd be curious if you could test the mm-pagealloc-irqpvec-v1r4 branch
ttps://git.kernel.org/pub/scm/linux/kernel/git/mel/linux.git . It's an
unfinished prototype I worked on a few weeks ago. I was going to revisit
in about a months time when 4.15-rc1 was out. I'd be interested in seeing
if it has a postive gain in normal page allocations without destroying
the performance of interrupt and softirq allocation contexts. The
interrupt/softirq context testing is crucial as that is something that
hurt us before when trying to improve page allocator performance.
Yes, I will test that once I get back in office (after netdev conference
and vacation).
Can you please elaborate in a few words about the idea behind the prototype?
Does it address page-allocator scalability issues, or only the rate of
single core page allocations?
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