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

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Message-ID: <55A7D955.5090203@citrix.com>
Date:	Thu, 16 Jul 2015 17:18:29 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
CC:	<ian.campbell@...rix.com>, <linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	<xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v2 13/20] xen/events: fifo: Make it running
 on 64KB granularity

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@...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?

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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