答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB

From: chengzhihao <chengzhihao1@huawei.com>
To: Richard Weinberger <richard@nod.at>
Cc: linux-mtd <linux-mtd@lists.infradead.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	"zhangyi \(F\)" <yi.zhang@huawei.com>
Subject: 答复: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB
Date: Thu, 1 Aug 2019 09:26:34 +0000	[thread overview]
Message-ID: <0B80F9D4116B2F4484E7279D5A66984F7A8A3A@dggemi524-mbx.china.huawei.com> (raw)
In-Reply-To: <1515821930.55881.1564651254907.JavaMail.zimbra@nod.at>

> You send this patch three times, I guess your mail setup has issues? :-)
Sorry, I thought I hadn't sent the first two e-mails. (The Patch work website refreshes slowly)

> Do you have numbers how many attempts were needed to get a free block?
I tested it dozens of times. The biggest number of attempts I've ever had so far is 6. In most cases, it only takes 2 or 3 times.

-----邮件原件-----
发件人: Richard Weinberger [mailto:richard@nod.at] 
发送时间: 2019年8月1日 17:21
收件人: chengzhihao <chengzhihao1@huawei.com>
抄送: zhangyi (F) <yi.zhang@huawei.com>; linux-mtd <linux-mtd@lists.infradead.org>; linux-kernel <linux-kernel@vger.kernel.org>
主题: Re: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number of attempts with polling while getting PEB

----- Ursprüngliche Mail -----
> Von: "chengzhihao1" <chengzhihao1@huawei.com>
> An: "richard" <richard@nod.at>, "yi zhang" <yi.zhang@huawei.com>
> CC: "linux-mtd" <linux-mtd@lists.infradead.org>, "linux-kernel" 
> <linux-kernel@vger.kernel.org>
> Gesendet: Donnerstag, 1. August 2019 11:13:20
> Betreff: 答复: [PATCH RFC] ubi: ubi_wl_get_peb: Replace a limited number 
> of attempts with polling while getting PEB

> I don't quite understand why a limited number of attempts have been 
> made to get a free PEB in ubi_wl_get_peb (in fastmap-wl.c). I proposed 
> this PATCH with reference to the implementation of ubi_wl_get_peb (in 
> wl.c). As far as I know, getting PEB by polling probably won't fall into soft-lockup.
> ubi_update_fastmap may add new tasks (including erase task or wl 
> taskk, wl tasks generally do not generate additional free PEBs) to 
> ubi->works, and produce_free_peb will eventually complete all tasks in 
> ubi->works or obtain an free PEB that can be filled into pool.

You send this patch three times, I guess your mail setup has issues? :-)

This is one of the darkest corners of Fastmap where things get messy.
The number of retry attempts was limited to avoid a live lock.

I agree that allowing only one retry is a little to few.
With nandsim, a small nand and a fast PC you can hit that.

Do you have numbers how many attempts were needed to get a free block?

Thanks,
//richard
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