Re: [PATCH net-next 1/4] unroll: add generic loop unroll helpers

Simon Horman
2025-02-09T11:07:31Z

On Thu, Feb 06, 2025 at 07:26:26PM +0100, Alexander Lobakin wrote:
> There are cases when we need to explicitly unroll loops. For example,
> cache operations, filling DMA descriptors on very high speeds etc.
> Add compiler-specific attribute macros to give the compiler a hint
> that we'd like to unroll a loop.
> Example usage:
>
> #define UNROLL_BATCH 8
>
> unrolled_count(UNROLL_BATCH)
> for (u32 i = 0; i < UNROLL_BATCH; i++)
> op(priv, i);
>
> Note that sometimes the compilers won't unroll loops if they think this
> would have worse optimization and perf than without unrolling, and that
> unroll attributes are available only starting GCC 8. For older compiler
> versions, no hints/attributes will be applied.
> For better unrolling/parallelization, don't have any variables that
> interfere between iterations except for the iterator itself.
>
> Co-developed-by: Jose E. Marchesi <jose.marchesi@oracle.com> # pragmas
> Signed-off-by: Jose E. Marchesi <jose.marchesi@oracle.com>
> Reviewed-by: Przemek Kitszel <przemyslaw.kitszel@intel.com>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com>

Hi Alexander,

This patch adds four variants of the unrolled helper. But as far as I can
tell the patch-set only makes use of one of them, unrolled_count().

I think it would be best if this patch only added helpers that are used.

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