Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932335AbXIEWun (ORCPT ); Wed, 5 Sep 2007 18:50:43 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756639AbXIEWuf (ORCPT ); Wed, 5 Sep 2007 18:50:35 -0400 Received: from barikada.upol.cz ([158.194.242.200]:59456 "EHLO barikada.upol.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753802AbXIEWue (ORCPT ); Wed, 5 Sep 2007 18:50:34 -0400 To: Nick Piggin Cc: Linux Kernel Mailing List , David Miller , Paul McKenney Subject: Fast path efficiency (Re: [rfc][patch] dynamic data structure switching) In-Reply-To: <20070902183618.GB13145@wotan.suse.de> References: <20070902182738.GA13145@wotan.suse.de> <20070902183618.GB13145@wotan.suse.de> Date: Thu, 6 Sep 2007 01:05:40 +0200 Message-Id: From: Oleg Verych Organization: Palacky University in Olomouc, experimental physics department X-OS: x86_64-pc-linux-glibc-debian Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1761 Lines: 69 * Sun, 2 Sep 2007 20:36:19 +0200 > I see, that in many places all pre-checks are done in negative form with resulting return or jump out. In this case, if function was called, what likely() path is? > +static void resize_pid_hash(void) > +{ > + unsigned int old_shift, new_shift; > + > + if (system_state != SYSTEM_RUNNING) > + return; > + > + old_shift = cur_pid_hash->shift; > + new_shift = ilog2(nr_pids * 2 - 1); > + if (new_shift == old_shift) > + return; > + > + if (!mutex_trylock(&dyn_pidhash.resize_mutex)) > + return; that one or this? == if (system_state == SYSTEM_RUNNING) { old_shift = cur_pid_hash->shift; new_shift = ilog2(nr_pids * 2 - 1); if (new_shift != old_shift && mutex_trylock(&dyn_pidhash.resize_mutex)) { == > + old_shift = cur_pid_hash->shift; > + new_shift = ilog2(nr_pids * 2 - 1); /* hope this repetition is needed by design */ ... > + mutex_unlock(&dyn_pidhash.resize_mutex); } What is more efficient in general sense, as opposed to s,3,2,1,0 Optimized? > + if (new_shift != old_shift) { > + struct pid_hash *ph, *ret; > + unsigned int idx = ph_cur_idx ^ 1; > + ph = &pid_hashes[idx]; > + if (!init_pid_hash(ph, new_shift)) { > + ph_cur_idx = idx; > + > + ret = dyn_data_replace(&dyn_pidhash, dd_transfer_pids, ph); > + BUG_ON(ret == ph); > + BUG_ON(ret != &pid_hashes[idx ^ 1]); > + /* XXX: kfree(ret->table) */ > + ret->shift = -1; > + ret->table = NULL; > + } > + } > + mutex_unlock(&dyn_pidhash.resize_mutex); > +} > + Thanks. ____ - 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/