[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Xen-devel] [PATCH for-4.12 v2 17/17] xen/arm: Track page accessed between batch of Set/Way operations

Hi Jan,

On 05/12/2018 08:37, Jan Beulich wrote:
On 04.12.18 at 21:26, <julien.grall@xxxxxxx> wrote:
At the moment, the implementation of Set/Way operations will go through
all the entries of the guest P2M and flush them. However, this is very
expensive and may render unusable a guest OS using them.

For instance, Linux 32-bit will use Set/Way operations during secondary
CPU bring-up. As the implementation is really expensive, it may be possible
to hit the CPU bring-up timeout.

To limit the Set/Way impact, we track what pages has been of the guest
has been accessed between batch of Set/Way operations. This is done
using bit[0] (aka valid bit) of the P2M entry.

This patch adds a new per-arch helper is introduced to perform actions just
before the guest is first unpaused. This will be used to invalidate the
P2M to track access from the start of the guest.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>


While we can spread d->creation_finished all over the code, the per-arch
helper to perform actions just before the guest is first unpaused can
bring a lot of benefit for both architecture. For instance, on Arm, the
flush to the instruction cache could be delayed until the domain is
first run. This would improve greatly the performance of creating guest.

Just the other day we had found a potential use on x86 as well
(even if I already don't recall anymore what it was), so the
addition is certainly helpful. It might have been nice to split
introduction of the interface from what you actually want it to
do on Arm, but irrespective of that
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
for the non-Arm pieces here.

I am expecting the patch to be merged in the next couple of weeks. But I am happy to split it if you need it before.


Julien Grall

Xen-devel mailing list



Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.