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

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Message-ID: <1411157769.13320.74.camel@snotra.buserror.net>
Date:	Fri, 19 Sep 2014 15:16:09 -0500
From:	Scott Wood <scottwood@...escale.com>
To:	Michael Neuling <mikey@...ling.org>
CC:	<greg@...ah.com>, <arnd@...db.de>, <mpe@...erman.id.au>,
	<benh@...nel.crashing.org>, <cbe-oss-dev@...ts.ozlabs.org>,
	<imunsie@...ibm.com>, <linux-kernel@...r.kernel.org>,
	<linuxppc-dev@...abs.org>, <jk@...abs.org>, <anton@...ba.org>,
	"Laurentiu Tudor" <Laurentiu.Tudor@...escale.com>
Subject: Re: [PATCH 03/15] powerpc/msi: Improve IRQ bitmap allocator

On Thu, 2014-09-18 at 18:26 +1000, 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(-)

This conflicts with (and partially duplicates)
http://patchwork.ozlabs.org/patch/381892/
which I have in my tree.  How should we handle it?

Laurentiu, from looking at the overlap between patches I see a problem
with your existing patch, regarding the out-of-irqs path and
msi_bitmap_free_hwirqs(), so one way or another that needs to get fixed
soon.

-Scott

> 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.
>  	 */
> -	offset = bitmap_find_free_region(bmp->bitmap, bmp->irq_count, order);
> +	offset = bitmap_find_next_zero_area(bmp->bitmap, bmp->irq_count, 0,
> +					    num, (1 << order) - 1);
> +	if (offset > bmp->irq_count)
> +		goto err;
> +	bitmap_set(bmp->bitmap, offset, num);
>  	spin_unlock_irqrestore(&bmp->lock, flags);
>  
>  	pr_debug("msi_bitmap: allocated 0x%x (2^%d) at offset 0x%x\n",
>  		 num, order, offset);
>  
>  	return offset;
> +err:
> +	spin_unlock_irqrestore(&bmp->lock, flags);
> +	return -ENOMEM;
>  }
> +EXPORT_SYMBOL(msi_bitmap_alloc_hwirqs);
>  
>  void msi_bitmap_free_hwirqs(struct msi_bitmap *bmp, unsigned int offset,
>  			    unsigned int num)
>  {
>  	unsigned long flags;
> -	int order = get_count_order(num);
>  
> -	pr_debug("msi_bitmap: freeing 0x%x (2^%d) at offset 0x%x\n",
> -		 num, order, offset);
> +	pr_debug("msi_bitmap: freeing 0x%x at offset 0x%x\n",
> +		 num, offset);
>  
>  	spin_lock_irqsave(&bmp->lock, flags);
> -	bitmap_release_region(bmp->bitmap, offset, order);
> +	bitmap_clear(bmp->bitmap, offset, num);
>  	spin_unlock_irqrestore(&bmp->lock, flags);
>  }
> +EXPORT_SYMBOL(msi_bitmap_free_hwirqs);
>  
>  void msi_bitmap_reserve_hwirq(struct msi_bitmap *bmp, unsigned int hwirq)
>  {


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