From nobody Mon Feb 9 09:17:00 2026 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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1A2AEC04A6A for ; Thu, 3 Aug 2023 12:00:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234787AbjHCMA0 (ORCPT ); Thu, 3 Aug 2023 08:00:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52380 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232363AbjHCMAX (ORCPT ); Thu, 3 Aug 2023 08:00:23 -0400 Received: from frasgout13.his.huawei.com (unknown [14.137.139.46]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 719EDE70 for ; Thu, 3 Aug 2023 05:00:20 -0700 (PDT) Received: from mail02.huawei.com (unknown [172.18.147.228]) by frasgout13.his.huawei.com (SkyGuard) with ESMTP id 4RGnDd3ND3z9xs5v for ; Thu, 3 Aug 2023 19:48:49 +0800 (CST) Received: from A2101119013HW2.china.huawei.com (unknown [10.81.221.240]) by APP2 (Coremail) with SMTP id GxC2BwB3d++6lstkfcs3AA--.61178S2; Thu, 03 Aug 2023 13:00:01 +0100 (CET) From: Petr Tesarik To: Christoph Hellwig , Marek Szyprowski , Robin Murphy , iommu@lists.linux.dev (open list:DMA MAPPING HELPERS), linux-kernel@vger.kernel.org (open list) Cc: Roberto Sassu , petr@tesarici.cz Subject: [PATCH v1] swiotlb: optimize get_max_slots() Date: Thu, 3 Aug 2023 13:59:41 +0200 Message-Id: <20230803115941.497-1-petrtesarik@huaweicloud.com> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: GxC2BwB3d++6lstkfcs3AA--.61178S2 X-Coremail-Antispam: 1UD129KBjvJXoW7tw47WFWkCF4ktw45Zw1kKrg_yoW8Jw4Upa 1xJr1rGayvqF1xAa4IyFs3KFyS93srJa9xXFZ0kryfu3W5tF4FqrWxK3yqq34FqrWvkF1a va4aqw4vyr43JrDanT9S1TB71UUUUUUqnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkE14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26r1j6r1xM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r1j 6r4UM28EF7xvwVC2z280aVAFwI0_Gr0_Cr1l84ACjcxK6I8E87Iv6xkF7I0E14v26r4j6r 4UJwAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0 I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r 4UM4x0Y48IcxkI7VAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwCY1x0264kExVAvwVAq 07x20xyl42xK82IYc2Ij64vIr41l4I8I3I0E4IkC6x0Yz7v_Jr0_Gr1lx2IqxVAqx4xG67 AKxVWUJVWUGwC20s026x8GjcxK67AKxVWUGVWUWwC2zVAF1VAY17CE14v26r1q6r43MIIY rxkI7VAKI48JMIIF0xvE2Ix0cI8IcVAFwI0_Jr0_JF4lIxAIcVC0I7IYx2IY6xkF7I0E14 v26r1j6r4UMIIF0xvE42xK8VAvwI8IcIk0rVWrZr1j6s0DMIIF0xvEx4A2jsIE14v26r1j 6r4UMIIF0xvEx4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x0JU2fO wUUUUU= X-CM-SenderInfo: hshw23xhvd2x3n6k3tpzhluzxrxghudrp/ X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Petr Tesarik Use a simple logical shift and increment to calculate the number of slots taken by the DMA segment boundary. At least GCC-13 is not able to optimize the expression, producing this horrible assembly code on x86: cmpq $-1, %rcx je .L364 addq $2048, %rcx shrq $11, %rcx movq %rcx, %r13 .L331: // rest of the function here... // after function epilogue and return: .L364: movabsq $9007199254740992, %r13 jmp .L331 After the optimization, the code looks more reasonable: shrq $11, %r11 leaq 1(%r11), %rbx Signed-off-by: Petr Tesarik --- kernel/dma/swiotlb.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-) diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c index 2b83e3ad9dca..a95d2ea2ae18 100644 --- a/kernel/dma/swiotlb.c +++ b/kernel/dma/swiotlb.c @@ -577,9 +577,7 @@ static inline phys_addr_t slot_addr(phys_addr_t start, = phys_addr_t idx) */ static inline unsigned long get_max_slots(unsigned long boundary_mask) { - if (boundary_mask =3D=3D ~0UL) - return 1UL << (BITS_PER_LONG - IO_TLB_SHIFT); - return nr_slots(boundary_mask + 1); + return (boundary_mask >> IO_TLB_SHIFT) + 1; } =20 static unsigned int wrap_area_index(struct io_tlb_mem *mem, unsigned int i= ndex) --=20 2.25.1