linux-kernel - Re: [PATCH] bcache: make stripe_size configurable and persistent for hardware raid5/6

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Message-ID: <611f98fc-222-8dd2-6b81-d570fb91fc@ewheeler.net>
Date:   Mon, 10 Jan 2022 15:30:24 -0800 (PST)
From:   Eric Wheeler <bcache@...ts.ewheeler.net>
To:     "Martin K. Petersen" <martin.petersen@...cle.com>
cc:     Kent Overstreet <kent.overstreet@...il.com>,
        Coly Li <colyli@...e.de>, linux-block@...r.kernel.org,
        Jonathan Corbet <corbet@....net>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:BCACHE (BLOCK LAYER CACHE)" <linux-bcache@...r.kernel.org>
Subject: Re: [PATCH] bcache: make stripe_size configurable and persistent
 for hardware raid5/6

On Mon, 10 Jan 2022, Martin K. Petersen wrote:
> > Ok so `git blame` shows that Kent added this to md/raid5.c in 
> > c78afc6261b (Kent Overstreet 2013-07-11 22:39:53 -0700 7526)
> 
> Yep.
> 
> > Do you think we should leave the md-specific
> > raid_partial_stripes_expensive setting and require users of RAID
> > controllers to set the bit themselves in bcache---or---remove all
> > raid_partial_stripes_expensive code and always treat writes as
> > "expensive" when `opt_io` is defined?
> 
> I'd prefer the latter since that was the very intent of exporting the
> device topology in an abstract and protocol-independent fashion.
> However, I don't know enough about bcache internals to know whether it
> is always the right choice, what the trade-offs are, etc.

I've not looked in detail, but I don't think its too difficult.

Do you know if io_opt can be configured on scsi devices that do not have 
io_opt provided by the controller?  If so, or if it would be easy to add, 
then configuring io_opt at the scsi layer is probably a better option so 
subsystems besides bcache would benefit.

What do you think?

--
Eric Wheeler


> 
> -- 
> Martin K. Petersen	Oracle Linux Engineering
>