linux-kernel - RE: [PATCH 21/29] ioat2,3: dynamically resize descriptor ring

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Message-ID: <129600E5E5FB004392DDC3FB599660D7B5548192@irsmsx504.ger.corp.intel.com>
Date:	Mon, 14 Sep 2009 16:00:24 +0100
From:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
To:	"Williams, Dan J" <dan.j.williams@...el.com>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: RE: [PATCH 21/29] ioat2,3: dynamically resize descriptor ring

Williams, Dan J wrote:
> Increment the allocation order of the descriptor ring every time we run
> out of descriptors up to a maximum of allocation order specified by the
> module parameter 'ioat_max_alloc_order'.  After each idle period
> decrement the allocation order to a minimum order of
> 'ioat_ring_alloc_order' (i.e. the default ring size, tunable as a module
> parameter).
> 
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---

Signed-off-by: Maciej Sosnowski <maciej.sosnowski@...el.com>

Just one thing:

> +static int ioat_ring_max_alloc_order = IOAT_MAX_ORDER;
> +module_param(ioat_ring_max_alloc_order, int, 0644);
> +MODULE_PARM_DESC(ioat_ring_max_alloc_order,
> +		 "ioat2+: upper limit for dynamic ring resizing (default: n=16)");
[...]
> --- a/drivers/dma/ioat/dma_v2.h
> +++ b/drivers/dma/ioat/dma_v2.h
> @@ -37,6 +37,8 @@ extern int ioat_pending_level;
>  #define IOAT_MAX_ORDER 16
>  #define ioat_get_alloc_order() \
>  	(min(ioat_ring_alloc_order, IOAT_MAX_ORDER))
> +#define ioat_get_max_alloc_order() \
> +	(min(ioat_ring_max_alloc_order, IOAT_MAX_ORDER))

Making the max_alloc_order a module parameter gives impression
that it can be modified by an user, including making it larger than default.
The default is however its maximum value, which may be confusing.
Why not to use parameter only as the upper limit?

Thanks,
Maciej--
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