xen gnttab problem

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xen gnttab problem

Christoph Kaminski
Hi

I can set the gnttab frames with gnttab_max_frames=256 as hypervisor
boot parameter.
It seems to be working for the dom0:

xen-diag gnttab_query_size 0
domid=0: nr_frames=1, max_nr_frames=256

but not for domU's:

xen-diag gnttab_query_size 2
domid=2: nr_frames=32, max_nr_frames=32

This causes problems in domU with lot of IO (example 5 virtual hd's as
NFS or/and SMB server). They hang if it want to use >32 frames.

it is possible that you set the value=32 for domU's in xen/kernel
config?

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Re: xen gnttab problem

Tomas Mozes
Hello,
if it's Xen version 4.10, then you need to set it in the domU configuration via max_grant_frames parameter. In older Xen it's a kernel parameter set globally.

Tomas

On Sat, Jun 30, 2018 at 12:14 PM, Christoph <[hidden email]> wrote:
Hi

I can set the gnttab frames with gnttab_max_frames=256 as hypervisor boot parameter.
It seems to be working for the dom0:

xen-diag gnttab_query_size 0
domid=0: nr_frames=1, max_nr_frames=256

but not for domU's:

xen-diag gnttab_query_size 2
domid=2: nr_frames=32, max_nr_frames=32

This causes problems in domU with lot of IO (example 5 virtual hd's as NFS or/and SMB server). They hang if it want to use >32 frames.

it is possible that you set the value=32 for domU's in xen/kernel config?

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------
Greetz

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Re: xen gnttab problem

Christoph Kaminski

Works... Thx a lot!

One question more: does it have disadvantages if I set the
max_grant_farmes to high? (I have it at 128 now. Should I look what it
uses max and set it corresponding to it?

Am 2018-06-30 13:43, schrieb Tomas Mozes:
> Hello,
> if it's Xen version 4.10, then you need to set it in the domU
> configuration via max_grant_frames parameter. In older Xen it's a
> kernel parameter set globally.
>
> Tomas
>
> On Sat, Jun 30, 2018 at 12:14 PM, Christoph <[hidden email]> wrote:
>

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Re: xen gnttab problem

Tomas Mozes
That's a good question I don't have answer for (the devs should answer this one). This page https://www.novell.com/support/kb/doc.php?id=7018590 even recommends 256 and it works for me fine, never observed a hang after setting it to this value. However the maximum gnttab I've seen was around 50-60, so 128 is probably enough. This of course depends on your usage, so it should be monitored and adjusted as needed. I think debian wanted to raise it to 64.

Tomas

On Mon, Jul 2, 2018 at 9:15 AM, Christoph <[hidden email]> wrote:

Works... Thx a lot!

One question more: does it have disadvantages if I set the max_grant_farmes to high? (I have it at 128 now. Should I look what it uses max and set it corresponding to it?


Am 2018-06-30 13:43, schrieb Tomas Mozes:
Hello,
if it's Xen version 4.10, then you need to set it in the domU
configuration via max_grant_frames parameter. In older Xen it's a
kernel parameter set globally.

Tomas

On Sat, Jun 30, 2018 at 12:14 PM, Christoph <[hidden email]> wrote:


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Greetz


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