netdev - Re: [PATCH net-next v2 1/9] unroll: add generic loop unroll helpers

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Message-ID: <66b571dc-19de-43ab-a10d-13cffdd82822@intel.com>
Date: Thu, 22 Aug 2024 17:15:25 +0200
From: Alexander Lobakin <aleksander.lobakin@...el.com>
To: Jakub Kicinski <kuba@...nel.org>
CC: Tony Nguyen <anthony.l.nguyen@...el.com>, <davem@...emloft.net>,
	<pabeni@...hat.com>, <edumazet@...gle.com>, <netdev@...r.kernel.org>,
	<przemyslaw.kitszel@...el.com>, <joshua.a.hay@...el.com>,
	<michal.kubiak@...el.com>, <nex.sw.ncis.osdt.itp.upstreaming@...el.com>,
	"Jose E . Marchesi" <jose.marchesi@...cle.com>
Subject: Re: [PATCH net-next v2 1/9] unroll: add generic loop unroll helpers

From: Jakub Kicinski <kuba@...nel.org>
Date: Tue, 20 Aug 2024 17:55:39 -0700

> On Mon, 19 Aug 2024 15:34:33 -0700 Tony Nguyen 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.
> 
> Please run the submissions thru get_maintainers

I always do that. get_maintainers.pl gives nobody for linux/unroll.h.

Thanks,
Olek