From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 0CD001BDAA6 for ; Tue, 6 Aug 2024 10:39:25 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722940767; cv=none; b=R2URbpgFFayxvGgwawHNTsvYr6eLQBT0xYlxdRW9y8T5M9jLRVxMgF/gtHIsJv9iCRiAIOIOibh3YCLkpomRG3SBCtf9su6BSrlmzoDYll6iZw+7rdbZj3aTuC2bW3BlqbxIGIH2JIJf4+3L1BjtubXKXG8l+j4UZxa5NPXY8tI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1722940767; c=relaxed/simple; bh=f3yrW3TgSKGlLolol72ndZGCbsVRSJQaOX3C228bnyY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=c4/HxhjmUmOhOuAkhHb7qVhEQZkv6p/xk2OOTdH3DyZfhQxY09wXBFvoZDxh1jUPh3RfboN9auGJ15DfyAC6DyhEuXAsV421EullGiQLZcO+lY80kIzoWip3SX2ShTtMRgSHvO0Z4DjBDLwuN1ZfOdt71pMWN47qTpwqLo6ego0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3E24CFEC; Tue, 6 Aug 2024 03:39:51 -0700 (PDT) Received: from [10.1.196.40] (e121345-lin.cambridge.arm.com [10.1.196.40]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9E0FC3F6A8; Tue, 6 Aug 2024 03:39:24 -0700 (PDT) Message-ID: Date: Tue, 6 Aug 2024 11:39:23 +0100 Precedence: bulk X-Mailing-List: iommu@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3] iommu: Optimize IOMMU UnMap To: Ashish Mhetre , will@kernel.org, joro@8bytes.org Cc: linux-arm-kernel@lists.infradead.org, iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-tegra@vger.kernel.org References: <20240805084106.214584-1-amhetre@nvidia.com> From: Robin Murphy Content-Language: en-GB In-Reply-To: <20240805084106.214584-1-amhetre@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 05/08/2024 9:41 am, Ashish Mhetre wrote: > The current __arm_lpae_unmap() function calls dma_sync() on individual > PTEs after clearing them. Overall unmap performance can be improved by > around 25% for large buffer sizes by combining the syncs for adjacent > leaf entries. > Optimize the unmap time by clearing all the leaf entries and issuing a > single dma_sync() for them. > Below is detailed analysis of average unmap latency(in us) with and > without this optimization obtained by running dma_map_benchmark for > different buffer sizes. > > UnMap Latency(us) > Size Without With % gain with > optimiztion optimization optimization > > 4KB 3 3 0 > 8KB 4 3.8 5 > 16KB 6.1 5.4 11.48 > 32KB 10.2 8.5 16.67 > 64KB 18.5 14.9 19.46 > 128KB 35 27.5 21.43 > 256KB 67.5 52.2 22.67 > 512KB 127.9 97.2 24.00 > 1MB 248.6 187.4 24.62 > 2MB 65.5 65.5 0 > 4MB 119.2 119 0.17 > > Signed-off-by: Ashish Mhetre > --- > Changes in V2: > - Updated the commit message to be imperative. > - Fixed ptep at incorrect index getting cleared for non-leaf entries. > > Changes in V3: > - Used loop-local variables and removed redundant function variables. > - Added check for zero-sized dma_sync in __arm_lpae_clear_pte(). > - Merged both patches into this single patch by adding check for a > NULL gather in __arm_lpae_unmap() itself. Yeah, that's cleaned up really nicely! Other than a nit that the subject ideally wants to be something more accurate like "iommu/io-pgtable-arm: Optimise non-coherent unmap" (sorry I forgot to mention that last time), Reviewed-by: Robin Murphy > --- > drivers/iommu/io-pgtable-arm.c | 31 +++++++++++++++++-------------- > 1 file changed, 17 insertions(+), 14 deletions(-) > > diff --git a/drivers/iommu/io-pgtable-arm.c b/drivers/iommu/io-pgtable-arm.c > index f5d9fd1f45bf..6fecf3d9fe67 100644 > --- a/drivers/iommu/io-pgtable-arm.c > +++ b/drivers/iommu/io-pgtable-arm.c > @@ -274,13 +274,13 @@ static void __arm_lpae_sync_pte(arm_lpae_iopte *ptep, int num_entries, > sizeof(*ptep) * num_entries, DMA_TO_DEVICE); > } > > -static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct io_pgtable_cfg *cfg) > +static void __arm_lpae_clear_pte(arm_lpae_iopte *ptep, struct io_pgtable_cfg *cfg, int num_entries) > { > + for (int i = 0; i < num_entries; i++) > + ptep[i] = 0; > > - *ptep = 0; > - > - if (!cfg->coherent_walk) > - __arm_lpae_sync_pte(ptep, 1, cfg); > + if (!cfg->coherent_walk && num_entries) > + __arm_lpae_sync_pte(ptep, num_entries, cfg); > } > > static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data, > @@ -654,26 +654,29 @@ static size_t __arm_lpae_unmap(struct arm_lpae_io_pgtable *data, > max_entries = ARM_LPAE_PTES_PER_TABLE(data) - unmap_idx_start; > num_entries = min_t(int, pgcount, max_entries); > > - while (i < num_entries) { > - pte = READ_ONCE(*ptep); > + /* Find and handle non-leaf entries */ > + for (i = 0; i < num_entries; i++) { > + pte = READ_ONCE(ptep[i]); > if (WARN_ON(!pte)) > break; > > - __arm_lpae_clear_pte(ptep, &iop->cfg); > - > if (!iopte_leaf(pte, lvl, iop->fmt)) { > + __arm_lpae_clear_pte(&ptep[i], &iop->cfg, 1); > + > /* Also flush any partial walks */ > io_pgtable_tlb_flush_walk(iop, iova + i * size, size, > ARM_LPAE_GRANULE(data)); > __arm_lpae_free_pgtable(data, lvl + 1, iopte_deref(pte, data)); > - } else if (!iommu_iotlb_gather_queued(gather)) { > - io_pgtable_tlb_add_page(iop, gather, iova + i * size, size); > } > - > - ptep++; > - i++; > } > > + /* Clear the remaining entries */ > + __arm_lpae_clear_pte(ptep, &iop->cfg, i); > + > + if (gather && !iommu_iotlb_gather_queued(gather)) > + for (int j = 0; j < i; j++) > + io_pgtable_tlb_add_page(iop, gather, iova + j * size, size); > + > return i * size; > } else if (iopte_leaf(pte, lvl, iop->fmt)) { > /*