Re: [PATCH v2] blk-throtl: optimize IOPS throttle for large IO scenarios

Tejun Heo wrote on 2021/7/31 12:07 上午:

On Fri, Jul 30, 2021 at 10:09:34AM +0800, brookxu wrote:

quoted

quoted

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@@ -877,10 +900,19 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw)
 	else
 		tg->bytes_disp[rw] = 0;
 
-	if (tg->io_disp[rw] >= io_trim)
+	if (tg_io_disp(tg, rw) >= io_trim) {

Instead of checking this in multiple places, would it be simpler to transfer
the atomic counters to the existing counters whenever we enter blk-throtl
and leave the rest of the code as-is?

If we do this, we need to do similar processing on the bio submission path and the bio
resubmission path in pending_timer. It seems that the code is more complicated?

Yeah, basically whenever we enter blk-throtl. Factored to a function,
calling it on entry should be fairly clean, right? I wonder whether it'd be
better to consolidate all atomic counter handling in a single location and
all it does is transferring whatever's accumulated to the usual counters.
Also, when you're reading & resetting the atomic counters, can you use a
pattern like the following?

  main_counter += atomic_xchg(counter, 0);

Right now, there's a race window between reading and resetting.

Yeah, thanks for your suggestion, I will submit the next version later.

Thanks.