linux-kernel - Re: [PATCH 03/15] powerpc/msi: Improve IRQ bitmap allocator

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Date:	Mon, 22 Sep 2014 11:29:10 +0300
From:	Laurentiu Tudor <b10716@...escale.com>
To:	Michael Neuling <mikey@...ling.org>, <greg@...ah.com>,
	<arnd@...db.de>, <mpe@...erman.id.au>, <benh@...nel.crashing.org>
CC:	<cbe-oss-dev@...ts.ozlabs.org>, <imunsie@...ibm.com>,
	<linux-kernel@...r.kernel.org>, <linuxppc-dev@...abs.org>,
	<jk@...abs.org>, <anton@...ba.org>
Subject: Re: [PATCH 03/15] powerpc/msi: Improve IRQ bitmap allocator

Hi Michael,

Minor comment inline.

On 09/18/2014 11:26 AM, Michael Neuling wrote:
> From: Ian Munsie <imunsie@....ibm.com>
> 
> Currently msi_bitmap_alloc_hwirqs() will round up any IRQ allocation requests
> to the nearest power of 2.  eg. ask for 5 IRQs and you'll get 8.  This wastes a
> lot of IRQs which can be a scarce resource.
> 
> For cxl we can require multiple IRQs for every contexts that is attached to the
> accelerator.  For AFU directed accelerators, there may be 1000s of contexts
> attached, hence we can easily run out of IRQs, especially if we are needlessly
> wasting them.
> 
> This changes the msi_bitmap_alloc_hwirqs() to allocate only the required number
> of IRQs, hence avoiding this wastage.
> 
> Signed-off-by: Ian Munsie <imunsie@....ibm.com>
> Signed-off-by: Michael Neuling <mikey@...ling.org>
> ---
>  arch/powerpc/sysdev/msi_bitmap.c | 18 +++++++++++++-----
>  1 file changed, 13 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/sysdev/msi_bitmap.c b/arch/powerpc/sysdev/msi_bitmap.c
> index 2ff6302..e001559 100644
> --- a/arch/powerpc/sysdev/msi_bitmap.c
> +++ b/arch/powerpc/sysdev/msi_bitmap.c
> @@ -24,28 +24,36 @@ int msi_bitmap_alloc_hwirqs(struct msi_bitmap *bmp, int num)
>  	 * This is fast, but stricter than we need. We might want to add
>  	 * a fallback routine which does a linear search with no alignment.
>  	 */

Is this comment still relevant (especially the part mentioning "fast")?

---
Best Regards, Laurentiu
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