From: Kalle Valo <kvalo@kernel.org>
To: Baochen Qiang <quic_bqiang@quicinc.com>
Cc: <ath11k@lists.infradead.org>, <linux-wireless@vger.kernel.org>,
<quic_bqiang@quicinc.com>
Subject: Re: [PATCH] wifi: ath11k: enable 36 bit mask for stream DMA
Date: Thu, 25 Jan 2024 16:38:11 +0000 (UTC) [thread overview]
Message-ID: <170620068905.500647.8187957964143425904.kvalo@kernel.org> (raw)
In-Reply-To: <20240123015201.28939-1-quic_bqiang@quicinc.com>
Baochen Qiang <quic_bqiang@quicinc.com> wrote:
> Currently 32 bit DMA mask is used, telling kernel to get us an DMA
> address under 4GB when mapping a buffer. This results in a very high
> CPU overhead in the case where IOMMU is disabled and more than 4GB
> system memory is installed. The reason is, with more than 4GB memory
> installed, kernel is likely to allocate a buffer whose physical
> address is above 4GB. While with IOMMU disabled, kernel has to involve
> SWIOTLB to map/unmap that buffer, which consumes lots of CPU cycles.
>
> We did hit an issue caused by the reason mentioned above: in a system
> that disables IOMMU and gets 8GB memory installed, a total of 40.5%
> CPU usage is observed in throughput test. CPU profiling shows nearly
> 60% of CPU cycles are consumed by SWIOTLB.
>
> By enabling 36 bit DMA mask, we can bypass SWIOTLB for any buffer
> whose physical address is below 64GB. There are two types of DMA mask
> within struct device, named dma_mask and coherent_dma_mask. Here we
> only enable 36 bit for dma_mask, because firmware crashes if
> coherent_dma_mask is also enabled, due to some unknown hardware
> limitations. This is acceptable because coherent_dma_mask is used for
> mapping a consistent DMA buffer, which generally does not happen in
> a hot path.
>
> With this change, the total CPU usage mentioned in above issue drops
> to 18.9%.
>
> Tested-on: WCN6855 hw2.1 PCI WLAN.HSP.1.1-03125-QCAHSPSWPL_V1_V2_SILICONZ_LITE-3.6510.23
> Tested-on: QCN9074 hw1.0 PCI WLAN.HK.2.7.0.1-01744-QCAHKSWPL_SILICONZ-1
> Tested-on: IPQ8074 hw2.0 AHB WLAN.HK.2.7.0.1-01744-QCAHKSWPL_SILICONZ-1
>
> Signed-off-by: Baochen Qiang <quic_bqiang@quicinc.com>
> Acked-by: Jeff Johnson <quic_jjohnson@quicinc.com>
> Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Patch applied to ath-next branch of ath.git, thanks.
dbd73acb22d8 wifi: ath11k: enable 36 bit mask for stream DMA
--
https://patchwork.kernel.org/project/linux-wireless/patch/20240123015201.28939-1-quic_bqiang@quicinc.com/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
prev parent reply other threads:[~2024-01-25 16:38 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-23 1:52 [PATCH] wifi: ath11k: enable 36 bit mask for stream DMA Baochen Qiang
2024-01-24 2:35 ` Jeff Johnson
2024-01-25 16:37 ` Kalle Valo
2024-01-25 16:38 ` Kalle Valo [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=170620068905.500647.8187957964143425904.kvalo@kernel.org \
--to=kvalo@kernel.org \
--cc=ath11k@lists.infradead.org \
--cc=linux-wireless@vger.kernel.org \
--cc=quic_bqiang@quicinc.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).