From: sashiko-bot@kernel.org
To: "Koichiro Den" <den@valinux.co.jp>
Cc: linux-pci@vger.kernel.org, linux-cxl@vger.kernel.org
Subject: Re: [PATCH 2/3] cxl: Account for link width in latency calculation
Date: Fri, 09 Oct 2026 05:01:20 +0000 [thread overview]
Message-ID: <sashiko-outbox-164861@kernel.org> (raw)
In-Reply-To: <20261009045452.1107921-3-den@valinux.co.jp>
> cxl_pci_get_latency() derives bandwidth from the per-lane speed returned
> by pcie_link_speed_mbps(), ignoring the negotiated link width. This
> overestimates the FlitLatency contribution for multi-lane links.
> Sections 2.11.3 and 2.11.4 of the Intel CXL Memory Device Software Guide
> describe the link bandwidth as the product of the negotiated speed and
> width.
>
> Replace pcie_link_speed_mbps() with pcie_link_bandwidth_mbps() and
> migrate both CXL callers (the only users of the API). The new helper
> obtains speed and width from a single Link Status read. The CXL
> bandwidth calculation no longer needs a separate width read and
> multiplication.
>
> While at it, make error handling more robust by converting PCI config
> read errors to negative errno values and checking for zero bandwidth
> before calculating latency.
>
> Fixes: 4d07a05397c8 ("cxl: Calculate and store PCI link latency for the downstream ports")
> Cc: stable@vger.kernel.org
> Signed-off-by: Koichiro Den <den@valinux.co.jp>
Sashiko has reviewed this patch and found no issues. It looks great!
--
Sashiko AI review · https://sashiko.dev/#/patchset/20261009045452.1107921-1-den@valinux.co.jp?part=2
next prev parent reply other threads:[~2026-10-09 5:01 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-09 4:54 [PATCH 0/3] cxl: Fix link latency calculations and QTG latency units Koichiro Den
2026-10-09 4:54 ` [PATCH 1/3] cxl/port: Convert PCIe link latency to nanoseconds Koichiro Den
2026-10-09 5:02 ` sashiko-bot
2026-10-09 4:54 ` [PATCH 2/3] cxl: Account for link width in latency calculation Koichiro Den
2026-10-09 5:01 ` sashiko-bot [this message]
2026-10-09 15:09 ` Bjorn Helgaas
2026-10-09 4:54 ` [PATCH 3/3] cxl/acpi: Convert QTG _DSM latencies to picoseconds Koichiro Den
2026-10-09 5:02 ` sashiko-bot
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