Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756025AbYK0OCz (ORCPT ); Thu, 27 Nov 2008 09:02:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752350AbYK0OCq (ORCPT ); Thu, 27 Nov 2008 09:02:46 -0500 Received: from www.tglx.de ([62.245.132.106]:58187 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752177AbYK0OCq (ORCPT ); Thu, 27 Nov 2008 09:02:46 -0500 Date: Thu, 27 Nov 2008 15:01:43 +0100 (CET) From: Thomas Gleixner To: eranian@googlemail.com cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, mingo@elte.hu, x86@kernel.org, andi@firstfloor.org, eranian@gmail.com, sfr@canb.auug.org.au Subject: Re: [patch 20/24] perfmon: system calls interface In-Reply-To: <492d0c0b.170e660a.15ba.ffffdabf@mx.google.com> Message-ID: References: <492d0c0b.170e660a.15ba.ffffdabf@mx.google.com> User-Agent: Alpine 2.00 (LFD 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1631 Lines: 68 On Wed, 26 Nov 2008, eranian@googlemail.com wrote: > +asmlinkage long sys_pfm_write(int fd, int uflags, > + int type, > + void __user *ureq, > + size_t sz) > +asmlinkage long sys_pfm_read(int fd, int uflags, > + int type, > + void __user *ureq, > + size_t sz) After looking at both I did a diff of the two functions: --- r.c 2008-11-27 14:27:54.000000000 +0100 +++ w.c 2008-11-27 14:27:52.000000000 +0100 @@ -36,10 +36,12 @@ ret = pfm_check_task_state(ctx, PFM_CMD_STOPPED, &flags); if (ret) goto skip; - switch(type) { + case PFM_RW_PMC: + ret = __pfm_write_pmcs(ctx, req, count); + break; case PFM_RW_PMD: - ret = __pfm_read_pmds(ctx, req, count); + ret = __pfm_write_pmds(ctx, req, count); break; default: PFM_DBG("invalid type=%d", type); @@ -48,12 +50,13 @@ skip: spin_unlock_irqrestore(&ctx->lock, flags); - if (copy_to_user(ureq, req, sz)) - ret = -EFAULT; - + /* + * This function may be on the critical path. + * We want to avoid the branch if unecessary. + */ if (fptr) kfree(fptr); error: pfm_release_ctx_from_fd(&cookie); return ret; } Both read and write are multiplexing syscalls already and 90% of the code is the same. case PFM_RD_PMC: case PFM_RD_PMD: case PFM_WR_PMC: case PFM_WR_PMD: would make them the same and safe a syscall and duplicated code. Thanks, tglx -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/