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Date: Wed, 10 Sep 2014 17:18:23 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Ming Lei <tom.leiming@...il.com>, Christoph Hellwig <hch@....de> CC: Jens Axboe <axboe@...nel.dk>, Linux Virtualization <virtualization@...ts.linux-foundation.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, "Michael S. Tsirkin" <mst@...hat.com> Subject: Re: [PATCH] virtio_blk: merge S/G list entries by default Il 07/09/2014 12:32, Ming Lei ha scritto: > It is a good idea to disable SG merge for vq incapable of indirect because > there are very limited direct descriptors. I think you mean _enabling_ SG merge if indirect descriptors are not there. > For vq capable of indirect, it should be better to not do SG merge at default > because: > > - from hypervisor view, no matter how many segments one req has, all are > submitted to host kernel by one syscall, such as readv/io_submit > > - host kernel still need to do the same merge again Here we agree. Paolo > From my test(virtio-blk over null_blk), looks enabling SG merge may cause > throughput a little drop(~3%). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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