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Re: [Xen-devel] [PATCH] xen: increase static dmesg buffer to 64K

To: Olaf Hering <olaf@xxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH] xen: increase static dmesg buffer to 64K
From: Keir Fraser <keir.xen@xxxxxxxxx>
Date: Mon, 18 Jul 2011 09:33:22 +0100
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Thread-topic: [Xen-devel] [PATCH] xen: increase static dmesg buffer to 64K
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On 18/07/2011 09:16, "Olaf Hering" <olaf@xxxxxxxxx> wrote:

> On Mon, Jul 18, Jan Beulich wrote:
>>>>> On 17.07.11 at 17:43, Olaf Hering <olaf@xxxxxxxxx> wrote:
>>> # HG changeset patch
>>> # User Olaf Hering <olaf@xxxxxxxxx>
>>> # Date 1310917380 -7200
>>> # Node ID c6cade90d47f32e19f529930ba9f9acfa69f065f
>>> # Parent  31dd84463eece20bd01c7aee22b52a0c06c67545
>>> xen: increase static dmesg buffer to 64K
>>> On large systems the static dmesg buffer will overflow the 16K buffer, early
>>> messages are lost. Increase the size to 64K to capture all lines on systems
>>> without serial console.
>> Please don't - on small systems it's a waste, and on even larger
>> systems it still won't help. If anything, the dynamic allocation may
>> need to happen earlier. As you probably saw, console_init_postirq()
>> already sizes the buffer dependent on the number of CPUs in the
>> system.
> I think conring_size= should be evaluated very early. Is there a way to
> allocate a range of mfns very early which can then be used for the dmesg
> buffer?

Are you actually losing messages because you can't allocate the larger
console ring early enough? It seems a bit unlikely, but possible I suppose.
Anyhow, the normal memory allocator is available plenty early enough. You'd
just need to do the allocation earlier than console_init_postirq(). Sometime
soon after the call to end_boot_allocator() would work nicely.

 -- Keir

> Olaf
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