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[2a01:c22:7bdd:8a00:ad81:1135:9a6d:a23f]) by smtp.googlemail.com with ESMTPSA id 4fb4d7f45d1cf-5733bebb6d5sm5222334a12.34.2024.05.12.15.08.01 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 12 May 2024 15:08:01 -0700 (PDT) Message-ID: <35fa38fc-9d1e-4a22-86dd-a4c9147d7f70@gmail.com> Date: Mon, 13 May 2024 00:08:01 +0200 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: r8169: transmit queue timeouts and IRQ masking To: Ken Milmore , netdev@vger.kernel.org Cc: nic_swsd@realtek.com References: <5181a634-fe25-45e7-803e-eb8737990e01@gmail.com> <940faa90-81db-40dc-8773-1720520b10ed@gmail.com> Content-Language: en-US From: Heiner Kallweit Autocrypt: addr=hkallweit1@gmail.com; keydata= xsFNBF/0ZFUBEAC0eZyktSE7ZNO1SFXL6cQ4i4g6Ah3mOUIXSB4pCY5kQ6OLKHh0FlOD5/5/ sY7IoIouzOjyFdFPnz4Bl3927ClT567hUJJ+SNaFEiJ9vadI6vZm2gcY4ExdIevYHWe1msJF MVE4yNwdS+UsPeCF/6CQQTzHc+n7DomE7fjJD5J1hOJjqz2XWe71fTvYXzxCFLwXXbBiqDC9 dNqOe5odPsa4TsWZ09T33g5n2nzTJs4Zw8fCy8rLqix/raVsqr8fw5qM66MVtdmEljFaJ9N8 /W56qGCp+H8Igk/F7CjlbWXiOlKHA25mPTmbVp7VlFsvsmMokr/imQr+0nXtmvYVaKEUwY2g 86IU6RAOuA8E0J5bD/BeyZdMyVEtX1kT404UJZekFytJZrDZetwxM/cAH+1fMx4z751WJmxQ J7mIXSPuDfeJhRDt9sGM6aRVfXbZt+wBogxyXepmnlv9K4A13z9DVLdKLrYUiu9/5QEl6fgI kPaXlAZmJsQfoKbmPqCHVRYj1lpQtDM/2/BO6gHASflWUHzwmBVZbS/XRs64uJO8CB3+V3fa cIivllReueGCMsHh6/8wgPAyopXOWOxbLsZ291fmZqIR0L5Y6b2HvdFN1Xhc+YrQ8TKK+Z4R mJRDh0wNQ8Gm89g92/YkHji4jIWlp2fwzCcx5+lZCQ1XdqAiHQARAQABzSZIZWluZXIgS2Fs bHdlaXQgPGhrYWxsd2VpdDFAZ21haWwuY29tPsLBjgQTAQgAOBYhBGxfqY/yOyXjyjJehXLe ig9U8DoMBQJf9GRVAhsDBQsJCAcCBhUKCQgLAgQWAgMBAh4BAheAAAoJEHLeig9U8DoMSycQ AJbfg8HZEK0ljV4M8nvdaiNixWAufrcZ+SD8zhbxl8GispK4F3Yo+20Y3UoZ7FcIidJWUUJL axAOkpI/70YNhlqAPMsuudlAieeYZKjIv1WV5ucNZ3VJ7dC+dlVqQdAr1iD869FZXvy91KhJ wYulyCf+s4T9YgmLC6jLMBZghKIf1uhSd0NzjyCqYWbk2ZxByZHgunEShOhHPHswu3Am0ftt ePaYIHgZs+Vzwfjs8I7EuW/5/f5G9w1vibXxtGY/GXwgGGHRDjFM7RSprGOv4F5eMGh+NFUJ TU9N96PQYMwXVxnQfRXl8O6ffSVmFx4H9rovxWPKobLmqQL0WKLLVvA/aOHCcMKgfyKRcLah 57vGC50Ga8oT2K1g0AhKGkyJo7lGXkMu5yEs0m9O+btqAB261/E3DRxfI1P/tvDZpLJKtq35 dXsj6sjvhgX7VxXhY1wE54uqLLHY3UZQlmH3QF5t80MS7/KhxB1pO1Cpcmkt9hgyzH8+5org +9wWxGUtJWNP7CppY+qvv3SZtKJMKsxqk5coBGwNkMms56z4qfJm2PUtJQGjA65XWdzQACib 2iaDQoBqGZfXRdPT0tC1H5kUJuOX4ll1hI/HBMEFCcO8++Bl2wcrUsAxLzGvhINVJX2DAQaF aNetToazkCnzubKfBOyiTqFJ0b63c5dqziAgzsFNBF/0ZFUBEADF8UEZmKDl1w/UxvjeyAeX kghYkY3bkK6gcIYXdLRfJw12GbvMioSguvVzASVHG8h7NbNjk1yur6AONfbUpXKSNZ0skV8V fG+ppbaY+zQofsSMoj5gP0amwbwvPzVqZCYJai81VobefTX2MZM2Mg/ThBVtGyzV3NeCpnBa 8AX3s9rrX2XUoCibYotbbxx9afZYUFyflOc7kEpc9uJXIdaxS2Z6MnYLHsyVjiU6tzKCiVOU KJevqvzPXJmy0xaOVf7mhFSNQyJTrZpLa+tvB1DQRS08CqYtIMxRrVtC0t0LFeQGly6bOngr ircurWJiJKbSXVstLHgWYiq3/GmCSx/82ObeLO3PftklpRj8d+kFbrvrqBgjWtMH4WtK5uN5 1WJ71hWJfNchKRlaJ3GWy8KolCAoGsQMovn/ZEXxrGs1ndafu47yXOpuDAozoHTBGvuSXSZo ythk/0EAuz5IkwkhYBT1MGIAvNSn9ivE5aRnBazugy0rTRkVggHvt3/7flFHlGVGpBHxFUwb /a4UjJBPtIwa4tWR8B1Ma36S8Jk456k2n1id7M0LQ+eqstmp6Y+UB+pt9NX6t0Slw1NCdYTW gJezWTVKF7pmTdXszXGxlc9kTrVUz04PqPjnYbv5UWuDd2eyzGjrrFOsJEi8OK2d2j4FfF++ AzOMdW09JVqejQARAQABwsF2BBgBCAAgFiEEbF+pj/I7JePKMl6Fct6KD1TwOgwFAl/0ZFUC GwwACgkQct6KD1TwOgxUfg//eAoYc0Vm4NrxymfcY30UjHVD0LgSvU8kUmXxil3qhFPS7KA+ y7tgcKLHOkZkXMX5MLFcS9+SmrAjSBBV8omKoHNo+kfFx/dUAtz0lot8wNGmWb+NcHeKM1eb nwUMOEa1uDdfZeKef/U/2uHBceY7Gc6zPZPWgXghEyQMTH2UhLgeam8yglyO+A6RXCh+s6ak Wje7Vo1wGK4eYxp6pwMPJXLMsI0ii/2k3YPEJPv+yJf90MbYyQSbkTwZhrsokjQEaIfjrIk3 rQRjTve/J62WIO28IbY/mENuGgWehRlTAbhC4BLTZ5uYS0YMQCR7v9UGMWdNWXFyrOB6PjSu Trn9MsPoUc8qI72mVpxEXQDLlrd2ijEWm7Nrf52YMD7hL6rXXuis7R6zY8WnnBhW0uCfhajx q+KuARXC0sDLztcjaS3ayXonpoCPZep2Bd5xqE4Ln8/COCslP7E92W1uf1EcdXXIrx1acg21 H/0Z53okMykVs3a8tECPHIxnre2UxKdTbCEkjkR4V6JyplTS47oWMw3zyI7zkaadfzVFBxk2 lo/Tny+FX1Azea3Ce7oOnRUEZtWSsUidtIjmL8YUQFZYm+JUIgfRmSpMFq8JP4VH43GXpB/S OCrl+/xujzvoUBFV/cHKjEQYBxo+MaiQa1U54ykM2W4DnHb1UiEf5xDkFd4= In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 12.05.2024 21:49, Ken Milmore wrote: > > > On 11/05/2024 17:31, Heiner Kallweit wrote: >> On 11.05.2024 00:29, Ken Milmore wrote: >>> >>> Reading this worries me though: >>> >>> https://docs.kernel.org/networking/napi.html >>> "napi_disable() and subsequent calls to the poll method only wait for the ownership of the instance to be released, not for the poll method to exit. >>> This means that drivers should avoid accessing any data structures after calling napi_complete_done()." >>> >> According to kernel doc napi_disable() waits. >> >> /** >> * napi_disable - prevent NAPI from scheduling >> * @n: NAPI context >> * >> * Stop NAPI from being scheduled on this context. >> * Waits till any outstanding processing completes. >> */ >> >>> Which seems to imply that the IRQ enable following napi_complete_done() is unguarded, and might race with the disable on an incoming poll. >>> Is that a possibility? >> >> Same documents states in section "Scheduling and IRQ masking": >> IRQ should only be unmasked after a successful call to napi_complete_done() >> So I think we should be fine. >> > > Nevertheless, it would be good if we could get away without the flag. > > I had started out with the assumption that an interrupt acknowledgement coinciding with some part of the work being done in rtl8169_poll() might be the cause of the problem. > So it seemed natural to try guarding the whole block by disabling interrupts at the beginning. > But this seems to work just as well: > > diff --git linux-source-6.1~/drivers/net/ethernet/realtek/r8169_main.c linux-source-6.1/drivers/net/ethernet/realtek/r8169_main.c > index 6e34177..353ce99 100644 > --- linux-source-6.1~/drivers/net/ethernet/realtek/r8169_main.c > +++ linux-source-6.1/drivers/net/ethernet/realtek/r8169_main.c > @@ -4659,8 +4659,10 @@ static int rtl8169_poll(struct napi_struct *napi, int budget) > > work_done = rtl_rx(dev, tp, budget); > > - if (work_done < budget && napi_complete_done(napi, work_done)) > + if (work_done < budget && napi_complete_done(napi, work_done)) { > + rtl_irq_disable(tp); > rtl_irq_enable(tp); > + } > > return work_done; > } > > On this basis, I assume the problem may actually involve some subtlety with the behaviour of the interrupt mask and status registers. > In the register dump in your original report the interrupt mask is set. So it seems rtl_irq_enable() was executed. I don't have an explanation why a previous rtl_irq_disable() makes a difference. Interesting would be whether it has to be a write to the interrupt mask register, or whether a write to any register is sufficient. > In addition, I'm not sure it is such a good idea to do away with disabling interrupts from within rtl8169_interrupt(). > This causes a modest, but noticeable increase in IRQ rate which I measured at around 3 to 7%, depending on whether the load is Tx or Rx heavy and also on the setting of gro_flush_timeout and napi_defer_hard_irqs. > > e.g. > Tx only test with iperf3, gro_flush_timeout=20000, napi_defer_hard_irqs=1: > Averaged 32343 vs 30165 interrupts per second, an increase of about 7%. > > Bidirectional test with with gro_flush_timeout=0, napi_defer_hard_irqs=0: > Averaged 82118 vs 79689 interrupts per second, an increase of about 3%. > > Given that these NICs are already fairly heavy on interrupt rate, it seems a shame to make them even worse! > > All in all I preferred the solution where we do all the interrupt disabling in rtl8169_interrupt(), notwithstanding that it may require a change to the interface of napi_schedule_prep(). I agree.