Re: [PATCH V14 14/24] mmc: block: Add CQE support
From: Ulf Hansson <hidden>
Date: 2017-11-28 11:21:03
Also in:
linux-mmc, lkml
On 21 November 2017 at 14:42, Adrian Hunter [off-list ref] wrote:
Add CQE support to the block driver, including:
- optionally using DCMD for flush requests
- "manually" issuing discard requests
- issuing read / write requests to the CQE
- supporting block-layer timeouts
- handling recovery
- supporting re-tuning
CQE offers 25% - 50% better random multi-threaded I/O. There is a slight
(e.g. 2%) drop in sequential read speed but no observable change to sequential
write.
CQE automatically sends the commands to complete requests. However it only
supports reads / writes and so-called "direct commands" (DCMD). Furthermore
DCMD is limited to one command at a time, but discards require 3 commands.
That makes issuing discards through CQE very awkward, but some CQE's don't
support DCMD anyway. So for discards, the existing non-CQE approach is
taken, where the mmc core code issues the 3 commands one at a time i.e.
mmc_erase(). Where DCMD is used, is for issuing flushes.
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>This looks good to me! I only have one, very minor comment. [...]
quoted hunk ↗ jump to hunk
@@ -370,10 +514,14 @@ static int mmc_mq_init_queue(struct mmc_queue *mq, int q_depth, static int mmc_mq_init(struct mmc_queue *mq, struct mmc_card *card, spinlock_t *lock) { + struct mmc_host *host = card->host; int q_depth; int ret; - q_depth = MMC_QUEUE_DEPTH; + if (mq->use_cqe) + q_depth = min_t(int, card->ext_csd.cmdq_depth, host->cqe_qdepth);
To make it clear why this is needed, could you please add some comment in the code? As I was trying to point out in the other reply about queue depth, for patch 13, this is weird to me. This may mean that we end up using queue_depth being less than MMC_QUEUE_DEPTH (64) for the CQE case. While in fact, in the CQE case the HW actually supports a bigger queue depth, comparing when not using CQE. Anyway, it seems like that will have to be a separate topic to discuss with the blkmq experts.
+ else + q_depth = MMC_QUEUE_DEPTH;
[...] Kind regards Uffe