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Date: Wed, 27 Apr 2011 09:13:39 -0700 From: Dave Hansen <dave@...ux.vnet.ibm.com> To: Jesse Gross <jesse@...ira.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, David Rientjes <rientjes@...gle.com> Subject: Re: [PATCH] flex_array: Avoid divisions when accessing elements. On Tue, 2011-04-26 at 13:41 -0700, Jesse Gross wrote: > On most architectures division is an expensive operation and > accessing an element currently requires four of them. This > performance penalty effectively precludes flex arrays from > being used on any kind of fast path. However, two of these > divisions can be handled at creation time and the others can > be replaced by a reciprocal divide, completely avoiding real > divisions on access. flex_array.c has a nice table for how many objects can be allocated: * Element size | Objects | Objects | * PAGE_SIZE=4k | 32-bit | 64-bit | * ---------------------------------| * 1 bytes | 4186112 | 2093056 | * 2 bytes | 2093056 | 1046528 | * 3 bytes | 1395030 | 697515 | * 4 bytes | 1046528 | 523264 | * 32 bytes | 130816 | 65408 | * 33 bytes | 126728 | 63364 | * 2048 bytes | 2044 | 1022 | * 2049 bytes | 1022 | 511 | * void * | 1046528 | 261632 | This patch changes that a bit. Would you mind updating it? -- Dave -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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