Messages in this thread | | | Date | Tue, 28 Mar 2023 10:41:02 -0700 | From | Luis Chamberlain <> | Subject | Re: 9p caching with cache=loose and cache=fscache |
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On Tue, Mar 28, 2023 at 01:53:49PM +0200, Christian Schoenebeck wrote: > Hi Luis, > > not sure which QEMU wiki page you are referring to. AFAIK we currently have 3 > QEMU wiki pages concerning 9p: > > 1. 9p documentation for users: > https://wiki.qemu.org/Documentation/9psetup
It was this one. I hadn't looked at the other ones.
> 2. 9p documentation for developers only: > https://wiki.qemu.org/Documentation/9p > > 3. How to setup an entire guest on top of a 9p root filesystem: > https://wiki.qemu.org/Documentation/9p_root_fs > > Only the latter wiki page mentions cache=loose at all: > > "To speedup things you can also consider to use e.g. cache=loose instead. > That will deploy a filesystem cache on guest side and reduces the amount > of 9p requests to hosts. As a consequence however guest might not > immediately see file changes performed on host side. So choose wisely upon > intended use case scenario. You can change between cache=mmap or e.g. > cache=loose at any time." > > Which I now changed to: > > "To speedup things you can also consider to use e.g. cache=loose instead.
My experience is that cache=loose is totally useless.
> That will deploy a filesystem cache on guest side and reduces the amount of > 9p requests to hosts. As a consequence however guest might not see file > changes performed on host side *at* *all*
I think that makes it pretty useless, aren't most setups on the guest read-only?
It is not about "may not see", just won't. For example I modified the Makefile and compiled a full kernel and even with those series of changes, the guest *minutes later* never saw any updates.
> (as Linux kernel's 9p client > currently does not revalidate for fs changes on host side at all, which is > planned to be changed on Linux kernel side soon though). So choose wisely > upon intended use case scenario. You can change between cache=mmap or e.g. > cache=loose at any time." > > On the user page it was already clearly mentioned though: > > "Mount the shared folder on guest using > > mount -t 9p -o trans=virtio test_mount /tmp/shared/ -oversion=9p2000.L,posixacl,msize=104857600,cache=none > > In the above example the folder /home/guest/9p_setup/ shared of the host > is shared with the folder /tmp/shared on the guest. We use no cache because > current caching mechanisms need more work and the results are not what you > would expect."
I got a wiki account now and I was the one who had clarified this.
Luis
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