On 3/5/24 01:13, Christian Loehle wrote:
On 05/03/2024 00:20, Bart Van Assche wrote:
On 3/4/24 12:16, Christian Loehle wrote:
- Higher cap is not always beneficial, we might place the task away
from the CPU where the interrupt handler is running, making it run
on an unboosted CPU which may have a bigger impact than the difference
between the CPU's capacity the task moved to. (Of course the boost will
then be reverted again, but a ping-pong every interval is possible).
In the above I see "the interrupt handler". Does this mean that the NVMe
controller in the test setup only supports one completion interrupt for
all completion queues instead of one completion interrupt per completion
queue? There are already Android phones and developer boards available
that support the latter, namely the boards equipped with a UFSHCI 4.0 controller.
No, both NVMe test setups have one completion interrupt per completion queue,
so this caveat doesn't affect them, higher capacity CPU is strictly better.
The UFS and both mmc setups (eMMC with CQE and sdcard) only have one completion
interrupt (on CPU0 on my setup).
I think that measurements should be provided in the cover letter for the
two types of storage controllers: one series of measurements for a
storage controller with a single completion interrupt and a second
series of measurements for storage controllers with one completion
interrupt per CPU.
FWIW you do gain an additional ~20% (in my specific setup) if you move the ufshcd
interrupt to a big CPU, too. Similarly for the mmc.
Unfortunately the infrastructure is far from being there for the scheduler to move the
interrupt to the same performance domain as the task, which is often optimal both in
terms of throughput and in terms of power.
I'll go looking for a stable testing platform with UFS as you mentioned, benefits of this
patch will of course be greatly increased.
I'm not sure whether making the completion interrupt follow the workload
is a good solution. I'm concerned that this would increase energy
consumption by keeping the big cores active longer than necessary. I
like this solution better (improves storage performance on at least
devices with a UFSHCI 3.0 controller): "[PATCH v2 0/2] sched: blk:
Handle HMP systems when completing IO"
(https://lore.kernel.org/linux-block/20240223155749.2958009-1-qyousef@xxxxxxxxxxx/).
Thanks,
Bart.
