Re: [Xen-ia64-devel] [Patch] improve response time at creating a guest

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

Hi Akio.
At first I'm agree with you that the constant may needs
to be reduced. The issue is what value is appropriate.

Do you know how long the hypercall takes?
Your description sounds like that the hypercall takes several
seconds. So havling it seems just to halve the time which still
stays the order of seconds. So it doesn't seem to solve your real
issue.

I suppose the hypercall should return in small time enough.
The problem is what "enough" is compared to what?
One candidate is vcpu time slice. Another possible candidate would
be time related to tcp timeout.

thanks,

On Thu, Jul 17, 2008 at 04:13:17PM +0900, Akio Takebe wrote:
> Hi,
> 
> When I create a guest having large memory,
> Some guests could not get network response for several seconds.
> The issue is caused by xencomm_privcmd_memory_reservation_op().
> To improve the response time, the attached patch reduces
> MEMORYOP_MAX_EXTENTS.
> 
> Signed-off-by: Akio Takebe <takebe_akio@xxxxxxxxxxxxxx>
> 
> Best Regards,
> 
> Akio Takebe

> diff -r 3643a33de277 arch/ia64/xen/xcom_privcmd.c
> --- a/arch/ia64/xen/xcom_privcmd.c    Mon Jun 30 16:14:04 2008 +0100
> +++ b/arch/ia64/xen/xcom_privcmd.c    Fri Jul 18 01:00:05 2008 +0900
> @@ -445,7 +445,7 @@ xencomm_privcmd_memory_reservation_op(pr
>                *   increase adoptively measuring hypercall time.
>                *   It might be over-kill.
>                */
> -#define MEMORYOP_MAX_EXTENTS (MEMORYOP_XENCOMM_LIMIT / 4)
> +#define MEMORYOP_MAX_EXTENTS (MEMORYOP_XENCOMM_LIMIT / 8)
>  
>               while (nr_extents > 0) {
>                       xen_ulong_t nr_tmp = nr_extents;

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-- 
yamahata

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