linux-kernel - Re: [PATCH] mmc: core: Add packed command for eMMC4.5 device

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Date:	Wed, 16 Nov 2011 03:51:26 -0800 (PST)
From:	merez@...eaurora.org
To:	"Seungwon Jeon" <tgih.jun@...sung.com>
Cc:	svenkatr@...com, linux-mmc@...r.kernel.org,
	"'Chris Ball'" <cjb@...top.org>, linux-kernel@...r.kernel.org,
	linux-samsung-soc@...r.kernel.org, kgene.kim@...sung.com,
	dh.han@...sung.com
Subject: Re: [PATCH] mmc: core: Add packed command for eMMC4.5 device

> +			if (reqs >= 2) {
> +				mmc_blk_packed_hdr_wrq_prep(mq->mqrq_cur, card, mq, reqs);
> +				if (rq_data_dir(rqc) == READ) {
> +					areq = &mq->mqrq_cur->mmc_active;
> +					mmc_wait_for_req(card->host, areq->mrq);
Packing read requests requires preparation of two requests. After sending
the header we wait for its completion before sending the next request
(mmc_wait_for_req is used). Therefore, if we try to pack 2 read requests
we might end up with worse performance in comparison to sending each
request by itself (which allows the preparation of one request while the
other is sent).
I suggest to check the size of the packed commands list and in case it is
less than 3 send the requests one by one. If you move mmc_blk_chk_packable
to queue.c after the first fetch this change should be very easy and can
be done by removing the requests from the packed_list and calling issue_fn
for each one of them.

Thanks,
Maya Erez
Consultant for Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum






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