Re: [Xen-devel] [PATCH v2 13/20] xen/events: fifo: Make it running on 64KB granularity

[Julien Grall <julien.grall@xxxxxxxxxx>]

Hi Stefano,

On 16/07/2015 16:43, Stefano Stabellini wrote:
> On Thu, 9 Jul 2015, Julien Grall wrote:
> > Only use the first 4KB of the page to store the events channel info. It
> > means that we will wast 60KB every time we allocate page for:
>                        ^ waste
>
> >       * control block: a page is allocating per CPU
> >       * event array: a page is allocating everytime we need to expand it
> >
> > I think we can reduce the memory waste for the 2 areas by:
> >
> >      * control block: sharing between multiple vCPUs. Although it will
> >      require some bookkeeping in order to not free the page when the CPU
> >      goes offline and the other CPUs sharing the page still there
> >
> >      * event array: always extend the array event by 64K (i.e 16 4K
> >      chunk). That would require more care when we fail to expand the
> >      event channel.
> But this is not implemented in this series, right?
Yes, it's some ideas to improve the code.

> > Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> > Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > Cc: David Vrabel <david.vrabel@xxxxxxxxxx>
> > ---
> >   drivers/xen/events/events_base.c | 2 +-
> >   drivers/xen/events/events_fifo.c | 2 +-
> >   2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
> > index 96093ae..858d2f6 100644
> > --- a/drivers/xen/events/events_base.c
> > +++ b/drivers/xen/events/events_base.c
> > @@ -40,11 +40,11 @@
> >   #include <asm/idle.h>
> >   #include <asm/io_apic.h>
> >   #include <asm/xen/pci.h>
> > -#include <xen/page.h>
> >   #endif
> >   #include <asm/sync_bitops.h>
> >   #include <asm/xen/hypercall.h>
> >   #include <asm/xen/hypervisor.h>
> > +#include <xen/page.h>
> >
> >   #include <xen/xen.h>
> >   #include <xen/hvm.h>
> Spurious change?
No, xen/page.h was only included for x86 before. Now, it's included for 
every architecture.
This is required in order to get XEN_PAGE_SIZE.

Regards,

--
Julien Grall

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