Date: Thu, 26 Mar 2015 00:43:27 -0700 From: Julian Hsiao <madoka@nyanisore.net> To: freebsd-virtualization@freebsd.org Subject: Re: Several bhyve quirks Message-ID: <mf0dau$6dj$1@ger.gmane.org> References: <5512D7E3.9060401@freebsd.org>
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On 2015-03-25 15:44:35 +0000, Peter Grehan said: > In 10.1, virtio-blk i/o is done sychronously in the context of the > guest vCPU exit. If it's a single vCPU guest, or the virtio-net > interrupt happens to be delivered to that vCPU, performance will suffer. > > A workaround is to use ahci-hd for the disk emulation and not > virtio-blk. The AHCI emulation does i/o in a dedicated thread and > doesn't block the vCPU thread. Thank you for your explanation and tips, Peter. I just tried changing virtio-blk -> ahci-hd and preliminary results are good. And now you've mentioned it, I do recall seeing slightly less performance degradation on guests with 2 vCPUs vs. ones with just one. I've always assumed virtio driver > emulated driver so it didn't occur to me to try ahci-hd. > The only workaround for 10.1 would be to use ahci-hd instead of > virtio-blk. The correct sector size will be reported there. I haven't had a chance to test this; next time I spin up a guest from scratch I'll try it out. > Try using the -W option to bhyve. This will force the bhyve virtio > code to advertize (non-standard) MSI interrupt capability which OpenBSD > will then use to allocate vectors. Unfortunately -W didn't help. This is not critical, however, and I'll ask around in the OpenBSD mailing list. Thanks again for your help. Julian Hsiaohelp
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