From patchwork Mon Oct 16 15:43:36 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Richard W.M. Jones" X-Patchwork-Id: 13423600 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 11671CDB474 for ; Mon, 16 Oct 2023 15:43:59 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1qsPku-0005Uw-6r; Mon, 16 Oct 2023 11:43:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qsPkt-0005UV-3a for qemu-devel@nongnu.org; Mon, 16 Oct 2023 11:43:43 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1qsPkr-00079X-9W for qemu-devel@nongnu.org; Mon, 16 Oct 2023 11:43:42 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1697471020; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type; bh=+YMFFZLHAZNohMJziJW/If5eTn+3J0Gx77R4mSLf7VY=; b=VCOP3xVXrwPJRengHp38MuryrdXt4iuSjnO0ArwLo7On3PEQPjEuJfM24G8I8FhtGWVrhe cOhT2TlVF2K3mN9HtFMeqnWMkrFmEf+r6iiuOT6hx7d6mXExp7t0sJOZ1T3ZromZBMgnmE Oue89D8NZzOOjphO4s+rrxS3X+XTPKE= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-547-ZLAYXjJJMl-24p-yxSDD-w-1; Mon, 16 Oct 2023 11:43:37 -0400 X-MC-Unique: ZLAYXjJJMl-24p-yxSDD-w-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id C1C8581D9E5 for ; Mon, 16 Oct 2023 15:43:36 +0000 (UTC) Received: from localhost (unknown [10.42.28.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8CCC0492BEE; Mon, 16 Oct 2023 15:43:36 +0000 (UTC) Date: Mon, 16 Oct 2023 16:43:36 +0100 From: "Richard W.M. Jones" To: qemu-devel@nongnu.org, pbonzini@redhat.com Subject: tcg_flush_jmp_cache replacing qatomic_set loop with memset Message-ID: <20231016154336.GA27462@redhat.com> MIME-Version: 1.0 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.9 Received-SPF: pass client-ip=170.10.129.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hey Paolo, Quick question. I'm sure the transformation below is *not* correct, because it doesn't preserve the invariant of the lockless structure. Is there a way to do this while maintaining correctness? For example putting barrier() after memset? (Note I'm also zeroing .pc which may be a problem.) The background to this is that I've been playing around with the very hot tb_lookup function. Increasing the size of the jump cache (which hasn't changed since, erm, 2005!), looks like it could improve performance, plus a few other changes which I'm playing with. However increasing the size causes profiles to be dominated by the loop in tcg_flush_jmp_cache, presumably because of all those serialized atomic ops. Rich. diff --git a/accel/tcg/translate-all.c b/accel/tcg/translate-all.c index 8cb6ad3511..6a21b3dba8 100644 --- a/accel/tcg/translate-all.c +++ b/accel/tcg/translate-all.c @@ -796,9 +796,7 @@ void tcg_flush_jmp_cache(CPUState *cpu) return; } - for (int i = 0; i < TB_JMP_CACHE_SIZE; i++) { - qatomic_set(&jc->array[i].tb, NULL); - } + memset(jc->array, 0, TB_JMP_CACHE_SIZE * sizeof jc->array[0]); } /* This is a wrapper for common code that can not use CONFIG_SOFTMMU */