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Re: [Xen-devel] increase evtchn limits

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] increase evtchn limits
From: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>
Date: Fri, 21 May 2010 11:52:14 -0700
Cc: Zhigang Wang <zhigang.x.wang@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On Fri, 21 May 2010 08:12:13 +0100
Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:

> On 21/05/2010 06:07, "Zhigang Wang" <zhigang.x.wang@xxxxxxxxxx> wrote:
> >>        unsigned long evtchn_pending[sizeof(unsigned long) * 8];
> >> 
> > I'm not sure, but it seems: 1024 for 32bit and 4096 for 64bit.
> > 
> > 32bit: 4 * (4 * 8) * 8 = 1024
> > 64bit: 8 * (8 * 8) * 8 = 4096
> This is correct. Which is why I wonder how many CPUs you are dealing
> with, and how many event channels are being allocated per CPU. 4096
> event channels ought to be plenty for dom0 bringup on even a very big
> system.
>  K.

My bad, it's ulong[], not sure why I thought it was uchar[]. So sorry
for the false alarm. I'm hitting BUG_ON(!test_bit(chn, s->evtchn_mask));
in bind_evtchn_to_cpu() and when I saw it on chn == 520, combined with
my thinking it was uchar, i made wrong conclusion. Apologies. Anyways,
I'll debug further.

But looking forward, I can see hitting limits of 4096 not too far in
future, so I think it will be a great idea to 'collapse the four IPIs
onto one event channel', perhaps next xen release.

Thanks again.

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