linux-kernel - Re: [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests.

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Message-ID: <20201207221433.GI20489@zn.tnic>
Date:   Mon, 7 Dec 2020 23:14:33 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ashish Kalra <ashish.kalra@....com>
Cc:     konrad.wilk@...cle.com, hch@....de, tglx@...utronix.de,
        mingo@...hat.com, hpa@...or.com, x86@...nel.org, luto@...nel.org,
        peterz@...radead.org, dave.hansen@...ux-intel.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        brijesh.singh@....com, Thomas.Lendacky@....com, Jon.Grimm@....com,
        rientjes@...gle.com
Subject: Re: [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV
 guests.

On Mon, Dec 07, 2020 at 10:06:24PM +0000, Ashish Kalra wrote:
> This is related to the earlier static adjustment of the SWIOTLB buffers
> as per guest memory size and Konrad's feedback on the same, as copied
> below : 
> 
> >>That is eating 128MB for 1GB, aka 12% of the guest memory allocated statically for this.
> >> 
> >> And for guests that are 2GB, that is 12% until it gets to 3GB when 
> >> it is 8% and then 6% at 4GB.
> >> 
> >> I would prefer this to be based on your memory count, that is 6% of 
> >> total memory.

So no rule of thumb and no measurements? Just a magic number 6.

Btw, pls trim the rest of the mail when you reply. Like I just did.
There's no need to leave text which you're not responding to, quoted.

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette