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Wed, 04 Dec 2024 21:21:50 +0100 Message-ID: <06edcab8-280d-4397-8df2-58a35eb094ec@engleder-embedded.com> Date: Wed, 4 Dec 2024 21:21:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Przemek Kitszel Cc: anthony.l.nguyen@intel.com, andrew+netdev@lunn.ch, netdev@vger.kernel.org, davem@davemloft.net, kuba@kernel.org, edumazet@google.com, pabeni@redhat.com, Gerhard Engleder , Vitaly Lifshits , "intel-wired-lan@lists.osuosl.org" References: <20241203202814.56140-1-gerhard@engleder-embedded.com> Content-Language: en-US From: Gerhard Engleder In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-AV-Do-Run: Yes X-Mailman-Original-DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=engleder-embedded.com; s=dkim11; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date:Message-ID:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=GirAyz2Vc6AyIWO7DCGREizNgX08C+P2Yh6QCGAaJaw=; b=fuT6POE0pV8AZkqh/tVR5YynqL ybsdQqZJkfj7yzQWM6Hb+vxiIHHM9chdE+auV+4txYxCGITqr4hBNupqwXlvbbKx+auJjGlMucEzg XZ3MRbMQAicd1V+mSnOBnkaVL7Mk54ygvfhPW5oJV2vNtBlwzLVE8z6kP4aaYq+/mDUk=; X-Mailman-Original-Authentication-Results: smtp3.osuosl.org; dmarc=pass (p=none dis=none) header.from=engleder-embedded.com X-Mailman-Original-Authentication-Results: smtp3.osuosl.org; dkim=pass (1024-bit key, unprotected) header.d=engleder-embedded.com header.i=@engleder-embedded.com header.a=rsa-sha256 header.s=dkim11 header.b=fuT6POE0 Subject: Re: [Intel-wired-lan] [PATCH net-next] e1000e: Fix real-time violations on link up X-BeenThere: intel-wired-lan@osuosl.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Intel Wired Ethernet Linux Kernel Driver Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-wired-lan-bounces@osuosl.org Sender: "Intel-wired-lan" On 04.12.24 11:10, Przemek Kitszel wrote: > On 12/3/24 21:28, Gerhard Engleder wrote: >> From: Gerhard Engleder >> >> From: Gerhard Engleder > > duplicated From: line Nervous fingers, sorry, will be fixed. >> >> Link down and up triggers update of MTA table. This update executes many >> PCIe writes and a final flush. Thus, PCIe will be blocked until all >> writes >> are flushed. As a result, DMA transfers of other targets suffer from >> delay >> in the range of 50us. This results in timing violations on real-time >> systems during link down and up of e1000e. >> >> A flush after a low enough number of PCIe writes eliminates the delay >> but also increases the time needed for MTA table update. The following >> measurements were done on i3-2310E with e1000e for 128 MTA table entries: >> >> Single flush after all writes: 106us >> Flush after every write:       429us >> Flush after every 2nd write:   266us >> Flush after every 4th write:   180us >> Flush after every 8th write:   141us >> Flush after every 16th write:  121us >> >> A flush after every 8th write delays the link up by 35us and the >> negative impact to DMA transfers of other targets is still tolerable. >> >> Execute a flush after every 8th write. This prevents overloading the >> interconnect with posted writes. As this also increases the time spent >> for >> MTA table update considerable this change is limited to PREEMPT_RT. > > hmm, why to limit this to PREEMPT_RT, the change sounds resonable also > for the standard kernel, at last for me > (perhaps with every 16th write instead) As Andrew argumented similar, I will remove the PREEMPT_RT dependency with the next version. This is not the hot path, so the additional delay of <<1ms for boot and interface up is negligible. > with that said, I'm fine with this patch as is too > >> >> Signed-off-by: Gerhard Engleder > > would be good to add link to your RFC > https://lore.kernel.org/netdev/f8fe665a-5e6c-4f95-b47a-2f3281aa0e6c@lunn.ch/T/ > > and also CC Vitaly who participated there (done), > same for IWL mailing list (also CCd), and use iwl-next tag for your > future contributions to intel ethernet Will be done. Thank you for the review! Gerhard