linux-kernel - Re: Question Regarding ERMS memcpy

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Date:   Mon, 6 Mar 2017 10:12:41 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Tony Luck <tony.luck@...el.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Question Regarding ERMS memcpy



On 06/03/17 12:28 AM, H. Peter Anvin wrote:
> On 03/05/17 23:01, Logan Gunthorpe wrote:
>>
>> On 05/03/17 12:54 PM, Borislav Petkov wrote:
>>> Logan, wanna give that a try, see if it takes care of your issue?
>>
>> Well honestly my issue was solved by fixing my kernel config. I have no
>> idea why I had optimize for size in there in the first place.
>>
> 
> Yes, to gcc "optimize for size" means exactly that... intended for cases
> where saving storage (e.g. ROM) or code download time is paramount.

I agree and understand, however placing a poorly performing _inline_
memcpy instead of a single call instruction to a performant memcopy
probably took more code space in the end. So like Linus, I just have to
scratch my head at the -Os optimization option.

Logan