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The intention of the following two patches is making users aware about 

the negative file I/O performance impact when using a very low value
 for 9P client parameter 'msize', which especially is the case if no
 'msize' parameter was supplied by the user with a 9P Linux client at all.
 
 All it does is logging a performance warning on host side (once) in
 that case. By setting 'msize' on client side to any value larger than
 8192 the performance warning will disappear.
 
 See https://wiki.qemu.org/Documentation/9psetup#msize for details.
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Merge remote-tracking branch 'remotes/cschoenebeck/tags/pull-9p-20200915' into staging

The intention of the following two patches is making users aware about
the negative file I/O performance impact when using a very low value
for 9P client parameter 'msize', which especially is the case if no
'msize' parameter was supplied by the user with a 9P Linux client at all.

All it does is logging a performance warning on host side (once) in
that case. By setting 'msize' on client side to any value larger than
8192 the performance warning will disappear.

See https://wiki.qemu.org/Documentation/9psetup#msize for details.

# gpg: Signature made Tue 15 Sep 2020 11:37:32 BST
# gpg:                using RSA key 96D8D110CF7AF8084F88590134C2B58765A47395
# gpg:                issuer "qemu_oss@crudebyte.com"
# gpg: Good signature from "Christian Schoenebeck <qemu_oss@crudebyte.com>" [unknown]
# gpg: WARNING: This key is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: ECAB 1A45 4014 1413 BA38  4926 30DB 47C3 A012 D5F4
#      Subkey fingerprint: 96D8 D110 CF7A F808 4F88  5901 34C2 B587 65A4 7395

* remotes/cschoenebeck/tags/pull-9p-20200915:
  9pfs: disable msize warning for synth driver
  9pfs: log warning if msize <= 8192

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Peter Maydell 2020-09-16 14:47:50 +01:00
parent de39a045bd c418f935ac
commit 8ee612722d
3 changed files with 15 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
fsdev/file-op-9p.h
View File

@ -64,6 +64,10 @@ typedef struct ExtendedOps {
*/
#define V9FS_REMAP_INODES 0x00000200
#define V9FS_FORBID_MULTIDEVS 0x00000400
/*
* Disables certain performance warnings from being logged on host side.
*/
#define V9FS_NO_PERF_WARN 0x00000800
#define V9FS_SEC_MASK 0x0000003C

2
hw/9pfs/9p-synth.c
View File

@ -541,6 +541,8 @@ static int synth_init(FsContext *ctx, Error **errp)
QLIST_INIT(&synth_root.child);
qemu_mutex_init(&synth_mutex);
ctx->export_flags |= V9FS_NO_PERF_WARN;
/* Add "." and ".." entries for root */
v9fs_add_dir_node(&synth_root, synth_root.attr->mode,
"..", synth_root.attr, synth_root.attr->inode);

9
hw/9pfs/9p.c
View File

@ -1353,6 +1353,15 @@ static void coroutine_fn v9fs_version(void *opaque)
goto out;
}
/* 8192 is the default msize of Linux clients */
if (s->msize <= 8192 && !(s->ctx.export_flags & V9FS_NO_PERF_WARN)) {
warn_report_once(
"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."
);
}
marshal:
err = pdu_marshal(pdu, offset, "ds", s->msize, &version);
if (err < 0) {