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Date: Mon, 7 Dec 2020 22:20:20 +0000 From: "Kalra, Ashish" <Ashish.Kalra@....com> To: Borislav Petkov <bp@...en8.de> CC: "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>, "hch@....de" <hch@....de>, "tglx@...utronix.de" <tglx@...utronix.de>, "mingo@...hat.com" <mingo@...hat.com>, "hpa@...or.com" <hpa@...or.com>, "x86@...nel.org" <x86@...nel.org>, "luto@...nel.org" <luto@...nel.org>, "peterz@...radead.org" <peterz@...radead.org>, "dave.hansen@...ux-intel.com" <dave.hansen@...ux-intel.com>, "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "Singh, Brijesh" <brijesh.singh@....com>, "Lendacky, Thomas" <Thomas.Lendacky@....com>, "Grimm, Jon" <Jon.Grimm@....com>, "rientjes@...gle.com" <rientjes@...gle.com> Subject: Re: [PATCH v7] swiotlb: Adjust SWIOTBL bounce buffer size for SEV guests. > On Dec 7, 2020, at 4:14 PM, Borislav Petkov <bp@...en8.de> wrote: > > 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. It is more of an approximation of the earlier static adjustment which was 128M for <1G guests, 256M for 1G-4G guests and 512M for >4G guests. Thanks, Ashish
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