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

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Date:	Thu, 16 Jul 2015 16:43:04 +0100
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	Julien Grall <julien.grall@...rix.com>
CC:	<xen-devel@...ts.xenproject.org>,
	<linux-arm-kernel@...ts.infradead.org>, <ian.campbell@...rix.com>,
	<stefano.stabellini@...citrix.com>, <linux-kernel@...r.kernel.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	"David Vrabel" <david.vrabel@...rix.com>
Subject: Re: [PATCH v2 13/20] xen/events: fifo: Make it running on 64KB
 granularity

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?


> Signed-off-by: Julien Grall <julien.grall@...rix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: David Vrabel <david.vrabel@...rix.com>
> ---
>  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?


> diff --git a/drivers/xen/events/events_fifo.c b/drivers/xen/events/events_fifo.c
> index ed673e1..d53c297 100644
> --- a/drivers/xen/events/events_fifo.c
> +++ b/drivers/xen/events/events_fifo.c
> @@ -54,7 +54,7 @@
>  
>  #include "events_internal.h"
>  
> -#define EVENT_WORDS_PER_PAGE (PAGE_SIZE / sizeof(event_word_t))
> +#define EVENT_WORDS_PER_PAGE (XEN_PAGE_SIZE / sizeof(event_word_t))
>  #define MAX_EVENT_ARRAY_PAGES (EVTCHN_FIFO_NR_CHANNELS / EVENT_WORDS_PER_PAGE)
>  
>  struct evtchn_fifo_queue {
> -- 
> 2.1.4
> 
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