Hi Leo, Leo Famulari <l...@famulari.name> writes:
> While using `guix system vm`, I noticed this warning. I think it's new, > maybe from the 5.2.0 update? > > ------ > qemu-system-x86_64: warning: 9p: degraded performance: a reasonable > high msize should be chosen on client/guest side (chosen msize is <= > 8192). See https://wiki.qemu.org/Documentation/9psetup#msize for > details. > ------ > > That web page suggests that we increase the virtio packet size when > declaring the 9p file-systems, I think in %linux-vm-file-systems of (gnu > system vm). The attached patch should fix it (it does for me at least!).
>From c720e68229322e5c38c0321b021e8d6430636111 Mon Sep 17 00:00:00 2001 From: Maxim Cournoyer <maxim.courno...@gmail.com> Date: Tue, 6 Apr 2021 17:37:33 -0400 Subject: [PATCH] system: vm: Set a larger value for the msize option of the 9p file system. Fixes <https://issues.guix.gnu.org/47225>. * gnu/system/vm.scm (mapping->file-system): Set the msize option to a value of 100 MiB (from the default 8 KiB). Reported-by: Leo Famulari <l...@famulari.name> --- gnu/system/vm.scm | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/gnu/system/vm.scm b/gnu/system/vm.scm index 3d0935b3af..f9cf39ae42 100644 --- a/gnu/system/vm.scm +++ b/gnu/system/vm.scm @@ -581,7 +581,15 @@ the operating system." (type "9p") (flags (if writable? '() '(read-only))) (options (string-append "trans=virtio" - (if writable? "" ",cache=loose"))) + (if writable? "" ",cache=loose") + ;; By default, the msize value is 8 KiB, which + ;; according to QEMU is insufficient and would + ;; degrade performance. The msize value should + ;; roughly match the bandwidth of the system's + ;; IO (see: + ;; https://wiki.qemu.org/Documentation/9psetup#msize). + ;; Use 100 MiB as a conservative default. + ",msize=104857600")) (check? #f) (create-mount-point? #t))))) -- 2.31.1
Thank you for the report, Maxim
