| Message ID | 20220817204634.1886-1-demi@invisiblethingslab.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Use direct I/O for loop devices | expand |
On 17.08.2022 22:46, Demi Marie Obenour wrote: > This is a huge performance improvement for two reasons: > > 1. It uses the filesystem’s asynchronous I/O support, rather than using > synchronous I/O. > 2. It bypasses the page cache, removing a redundant layer of caching and > associated overhead. > --- > tools/hotplug/Linux/block | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/hotplug/Linux/block b/tools/hotplug/Linux/block > index 2691b56951c9b82094471a141b9e0bed04abb929..75785f3a5422c4a5f962a4cd4f6acae5080d036d 100644 > --- a/tools/hotplug/Linux/block > +++ b/tools/hotplug/Linux/block > @@ -330,7 +330,7 @@ mount it read-write in a guest domain." > else > roflag='' > fi > - do_or_die losetup $roflag "$loopdev" "$file" > + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file" I guess you want to first check (maybe in tools/configure) that losetup actually supports that option. The old-ish one I'm looking at doesn't, according to its --help output at least. Jan
On Thu, Aug 18, 2022 at 09:02:11AM +0200, Jan Beulich wrote: > On 17.08.2022 22:46, Demi Marie Obenour wrote: > > This is a huge performance improvement for two reasons: > > > > 1. It uses the filesystem’s asynchronous I/O support, rather than using > > synchronous I/O. > > 2. It bypasses the page cache, removing a redundant layer of caching and > > associated overhead. > > --- > > tools/hotplug/Linux/block | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/tools/hotplug/Linux/block b/tools/hotplug/Linux/block > > index 2691b56951c9b82094471a141b9e0bed04abb929..75785f3a5422c4a5f962a4cd4f6acae5080d036d 100644 > > --- a/tools/hotplug/Linux/block > > +++ b/tools/hotplug/Linux/block > > @@ -330,7 +330,7 @@ mount it read-write in a guest domain." > > else > > roflag='' > > fi > > - do_or_die losetup $roflag "$loopdev" "$file" > > + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file" > > I guess you want to first check (maybe in tools/configure) that losetup > actually supports that option. The old-ish one I'm looking at doesn't, > according to its --help output at least. What version are you referring to? In Qubes OS the current plan is to use a block “script” written in C, to improve performance and (when combined with kernel patches) eliminate race conditions. This code could be made a wrapper for the C version.
On 18.08.2022 16:04, Demi Marie Obenour wrote: > On Thu, Aug 18, 2022 at 09:02:11AM +0200, Jan Beulich wrote: >> On 17.08.2022 22:46, Demi Marie Obenour wrote: >>> --- a/tools/hotplug/Linux/block >>> +++ b/tools/hotplug/Linux/block >>> @@ -330,7 +330,7 @@ mount it read-write in a guest domain." >>> else >>> roflag='' >>> fi >>> - do_or_die losetup $roflag "$loopdev" "$file" >>> + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file" >> >> I guess you want to first check (maybe in tools/configure) that losetup >> actually supports that option. The old-ish one I'm looking at doesn't, >> according to its --help output at least. > > What version are you referring to? The tool itself doesn't recognize --version. It originates from util-linux 2.19.1 from all I can tell. > In Qubes OS the current plan is to use a block “script” written in C, to > improve performance and (when combined with kernel patches) eliminate > race conditions. This code could be made a wrapper for the C version. Is this relevant here in some way I don't recognize, or did you say this only to provide some further background info? Jan
On Thu, Aug 18, 2022 at 04:12:10PM +0200, Jan Beulich wrote: > On 18.08.2022 16:04, Demi Marie Obenour wrote: > > On Thu, Aug 18, 2022 at 09:02:11AM +0200, Jan Beulich wrote: > >> On 17.08.2022 22:46, Demi Marie Obenour wrote: > >>> --- a/tools/hotplug/Linux/block > >>> +++ b/tools/hotplug/Linux/block > >>> @@ -330,7 +330,7 @@ mount it read-write in a guest domain." > >>> else > >>> roflag='' > >>> fi > >>> - do_or_die losetup $roflag "$loopdev" "$file" > >>> + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file" > >> > >> I guess you want to first check (maybe in tools/configure) that losetup > >> actually supports that option. The old-ish one I'm looking at doesn't, > >> according to its --help output at least. > > > > What version are you referring to? > > The tool itself doesn't recognize --version. It originates from > util-linux 2.19.1 from all I can tell. I see. Qubes OS doesn’t need to support such old versions. Are you referring to > > In Qubes OS the current plan is to use a block “script” written in C, to > > improve performance and (when combined with kernel patches) eliminate > > race conditions. This code could be made a wrapper for the C version. > > Is this relevant here in some way I don't recognize, or did you say this > only to provide some further background info? If the C code becomes part of the toolstack it would avoid needing to call into losetup.
On Wed, Aug 17, 2022 at 04:46:34PM -0400, Demi Marie Obenour wrote: > This is a huge performance improvement for two reasons: > > 1. It uses the filesystem’s asynchronous I/O support, rather than using > synchronous I/O. > 2. It bypasses the page cache, removing a redundant layer of caching and > associated overhead. Cross-posting here just in case: this patch breaks block script on devices with 4k block size, at least with some util-linux versions. More details at https://github.com/QubesOS/qubes-issues/issues/7828 > --- > tools/hotplug/Linux/block | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/tools/hotplug/Linux/block b/tools/hotplug/Linux/block > index 2691b56951c9b82094471a141b9e0bed04abb929..75785f3a5422c4a5f962a4cd4f6acae5080d036d 100644 > --- a/tools/hotplug/Linux/block > +++ b/tools/hotplug/Linux/block > @@ -330,7 +330,7 @@ mount it read-write in a guest domain." > else > roflag='' > fi > - do_or_die losetup $roflag "$loopdev" "$file" > + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file" > xenstore_write "$XENBUS_PATH/node" "$loopdev" > write_dev "$loopdev" > release_lock "block" > -- > Sincerely, > Demi Marie Obenour (she/her/hers) > Invisible Things Lab >
diff --git a/tools/hotplug/Linux/block b/tools/hotplug/Linux/block index 2691b56951c9b82094471a141b9e0bed04abb929..75785f3a5422c4a5f962a4cd4f6acae5080d036d 100644 --- a/tools/hotplug/Linux/block +++ b/tools/hotplug/Linux/block @@ -330,7 +330,7 @@ mount it read-write in a guest domain." else roflag='' fi - do_or_die losetup $roflag "$loopdev" "$file" + do_or_die losetup --direct-io=on $roflag "$loopdev" "$file" xenstore_write "$XENBUS_PATH/node" "$loopdev" write_dev "$loopdev" release_lock "block"