From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Christian Schoenebeck Subject: Re: [virtio-comment] Re: [PATCH v2 0/2] Add VIRTIO_RING_F_LARGE_INDIRECT_DESC Date: Thu, 09 Dec 2021 13:33:20 +0100 Message-ID: <2346601.RvB5glhVSD@silver> In-Reply-To: <877dcft8u0.fsf@redhat.com> References: <877dcft8u0.fsf@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" To: Cornelia Huck Cc: Stefan Hajnoczi , virtio-comment@lists.oasis-open.org, Greg Kurz List-ID: On Mittwoch, 8. Dezember 2021 16:28:07 CET Cornelia Huck wrote: > On Wed, Dec 08 2021, Stefan Hajnoczi wrote: > > On Wed, Dec 08, 2021 at 01:26:54PM +0100, Christian Schoenebeck wrote: > >> One more thought: what about making the new 'queue_indirect_size' config > >> field 32 bit wide instead of 16 bit? That would easily mitigate the > >> issue of the aggregated limit discussed here, and would in general be > >> more future safe, i.e. considering that there might be either > >> nested/multi-level indirect descriptor tables or chained tables in > >> future? The cost would be low, right?> > > The MMIO transport has 32-bit fields, so there doesn't seem to be a > > strict requirement to use 16 bits for descriptor counts. > > > > I think you're right that the cost is low. Usually it's the access > > itself that carries a cost (a VM exit or bus transaction) and 2 vs 4 > > byte transfers don't really matter. > > For ccw, I think we'd simply include the value in a control block, and > it does not really matter whether that control block is 2 bytes > longer. So, no objection from me. Sounds like a plan! I will send a new version next week. Thanks guys! Best regards, Christian Schoenebeck