QEMU warning about performance

DoneSubmitted by Leo Famulari.
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2 participants
  • Leo Famulari
  • Maxim Cournoyer
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Leo Famulari wrote on 18 Mar 07:25 +0100
(address . bug-guix@gnu.org)
YFLyVjT+hOYHvMS2@jasmine.lan
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#msizefor details.------
That web page suggests that we increase the virtio packet size whendeclaring the 9p file-systems, I think in %linux-vm-file-systems of (gnusystem vm).
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Leo Famulari wrote on 6 Apr 21:45 +0200
(no subject)
(address . control@debbugs.gnu.org)
YGy6Yp2cwCqk6PKw@jasmine.lan
block 47297 with 47225
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Maxim Cournoyer wrote on 6 Apr 23:42 +0200
Re: bug#47225: QEMU warning about performance
(name . Leo Famulari)(address . leo@famulari.name)(address . 47225@debbugs.gnu.org)
87zgybnl8o.fsf@gmail.com
Hi Leo,
Leo Famulari <leo@famulari.name> writes:
Toggle quote (14 lines)> 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 2001From: Maxim Cournoyer <maxim.cournoyer@gmail.com>Date: Tue, 6 Apr 2021 17:37:33 -0400Subject: [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 of100 MiB (from the default 8 KiB).
Reported-by: Leo Famulari <leo@famulari.name>--- gnu/system/vm.scm | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
Toggle diff (23 lines)diff --git a/gnu/system/vm.scm b/gnu/system/vm.scmindex 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
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Leo Famulari wrote on 7 Apr 00:15 +0200
(name . Maxim Cournoyer)(address . maxim.cournoyer@gmail.com)(address . 47225@debbugs.gnu.org)
YGzdd2ey7wbrzN+h@jasmine.lan
On Tue, Apr 06, 2021 at 05:42:15PM -0400, Maxim Cournoyer wrote:
Toggle quote (13 lines)> From c720e68229322e5c38c0321b021e8d6430636111 Mon Sep 17 00:00:00 2001> From: Maxim Cournoyer <maxim.cournoyer@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 <leo@famulari.name>
Thanks! I'll test and push along with the next kernel update (that'swhen I noticed this warning). Feel free to push sooner if you like.
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Maxim Cournoyer wrote on 7 Apr 02:42 +0200
(name . Leo Famulari)(address . leo@famulari.name)(address . 47225@debbugs.gnu.org)
87v98zncw1.fsf@gmail.com
Hi Leo!
Leo Famulari <leo@famulari.name> writes:
Toggle quote (17 lines)> On Tue, Apr 06, 2021 at 05:42:15PM -0400, Maxim Cournoyer wrote:>> From c720e68229322e5c38c0321b021e8d6430636111 Mon Sep 17 00:00:00 2001>> From: Maxim Cournoyer <maxim.cournoyer@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 <leo@famulari.name>>> Thanks! I'll test and push along with the next kernel update (that's> when I noticed this warning). Feel free to push sooner if you like.
I hope I'm timely; I've made a revised version of the patch, that shouldcover more cases (and actually uses 100 MiB rather than 1 MiB :-)).
Thank you,
From eb600c4ffbc8016709db9471f9dc0be1d60167a7 Mon Sep 17 00:00:00 2001From: Maxim Cournoyer <maxim.cournoyer@gmail.com>Date: Tue, 6 Apr 2021 17:37:33 -0400Subject: [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 (%default-msize-value): New variable.(%linux-vm-file-systems): Use it as the value of the msize option.(mapping->file-system): Likewise.
Reported-by: Leo Famulari <leo@famulari.name>--- gnu/system/vm.scm | 18 ++++++++++++++---- 1 file changed, 14 insertions(+), 4 deletions(-)
Toggle diff (57 lines)diff --git a/gnu/system/vm.scm b/gnu/system/vm.scmindex 3d0935b3af..1efae7ff06 100644--- a/gnu/system/vm.scm+++ b/gnu/system/vm.scm@@ -88,6 +88,13 @@ ;;; ;;; Code: +;; 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.+(define %default-msize-value (* 100 (expt 2 20))) ;100 MiB+ (define %linux-vm-file-systems ;; File systems mounted for 'derivation-in-linux-vm'. These are shared with ;; the host over 9p.@@ -103,21 +110,23 @@ (type "9p") (needed-for-boot? #t) (flags '(read-only))- (options "trans=virtio,cache=loose")+ (options (format #f "trans=virtio,cache=loose,msize=~a"+ %default-msize-value)) (check? #f)) (file-system (mount-point "/xchg") (device "xchg") (type "9p") (needed-for-boot? #t)- (options "trans=virtio")+ (options (format #f "trans=virtio,msize=~a" %default-msize-value)) (check? #f)) (file-system (mount-point "/tmp") (device "tmp") (type "9p") (needed-for-boot? #t)- (options "trans=virtio,cache=loose")+ (options (format #f "trans=virtio,cache=loose,msize=~a"+ %default-msize-value)) (check? #f)))) (define not-config?@@ -581,7 +590,8 @@ the operating system." (type "9p") (flags (if writable? '() '(read-only))) (options (string-append "trans=virtio"- (if writable? "" ",cache=loose")))+ (if writable? "" ",cache=loose")+ ",msize=" (number->string %default-msize-value))) (check? #f) (create-mount-point? #t))))) -- 2.31.1
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Leo Famulari wrote on 7 Apr 19:46 +0200
(name . Maxim Cournoyer)(address . maxim.cournoyer@gmail.com)(address . 47225@debbugs.gnu.org)
YG3v7y5euYkA10Wz@jasmine.lan
On Tue, Apr 06, 2021 at 08:42:38PM -0400, Maxim Cournoyer wrote:
Toggle quote (3 lines)> I hope I'm timely; I've made a revised version of the patch, that should> cover more cases (and actually uses 100 MiB rather than 1 MiB :-)).
Yes, you're in time :) Thanks for the revised patch.
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Leo Famulari wrote on 8 Apr 21:17 +0200
(name . Maxim Cournoyer)(address . maxim.cournoyer@gmail.com)(address . 47225-done@debbugs.gnu.org)
YG9W41of3m0DysgM@jasmine.lan
On Tue, Apr 06, 2021 at 08:42:38PM -0400, Maxim Cournoyer wrote:
Toggle quote (20 lines)> I hope I'm timely; I've made a revised version of the patch, that should> cover more cases (and actually uses 100 MiB rather than 1 MiB :-)).> > Thank you,>
> From eb600c4ffbc8016709db9471f9dc0be1d60167a7 Mon Sep 17 00:00:00 2001> From: Maxim Cournoyer <maxim.cournoyer@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 (%default-msize-value): New variable.> (%linux-vm-file-systems): Use it as the value of the msize option.> (mapping->file-system): Likewise.> > Reported-by: Leo Famulari <leo@famulari.name>
Pushed as bdc96f6e0e7fbf502f368d3381297ec0b75216d7
Thanks!
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