linux-kernel - Re: [PATCH v4 1/3]mmc: set max_discard

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Message-Id: <201102141313.52132.arnd@arndb.de>
Date:	Mon, 14 Feb 2011 13:13:51 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	"Dong, Chuanxiao" <chuanxiao.dong@...el.com>
Cc:	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	"cjb@...top.org" <cjb@...top.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"adrian.hunter@...ia.com" <adrian.hunter@...ia.com>
Subject: Re: [PATCH v4 1/3]mmc: set max_discard_sectors value for mmc queue

On Monday 14 February 2011, Dong, Chuanxiao wrote:
> When I do trim with a 32GB eMMC card in my platform, sometimes I can get the 10s
> timeout errors but sometimes not. I am not much clear about the "discarding partial
> AU will take a lot longer". If this action is hide for driver, then I think from 
> driver side, the UINT_MAX value for max_discard_sectors will be OK. But if this action
> sometimes need driver to wait for some hardware interrupt, then I think the UINT_MAX
> value is not preferred.
>
> Arnd, have any suggestion of dealing this? What I thought is using other value
> instead of using UINT_MAX.

I'm not too familiar with the eMMC spec, but it should have a way to calculate
a maximum trim timeout like SD 3.0 does for AU erases. When I've seen the timeouts
with SDHCI (missing your patch), it was always a bug in the driver, and the
erase was already completed before the driver even started waiting for the
interrupt.

10 seconds still sounds like a reasonable timeout, and we should probably
not issue any requests that might take longer than that, so I think the
interesting question is how to determine a good value for pref_erase,
so we can still take your patch.

	Arnd
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