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([2600:1700:e321:62f0:da43:aeff:fecc:bfd5]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-7fc9c2d6022sm1457080a12.1.2024.11.28.07.30.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 28 Nov 2024 07:30:24 -0800 (PST) Sender: Guenter Roeck Message-ID: <2cb25f89-50b9-4e72-9b18-bee78e09c57c@roeck-us.net> Date: Thu, 28 Nov 2024 07:30:22 -0800 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [patch 2/2] timekeeping: Always check for negative motion To: Thomas Gleixner , John Stultz Cc: LKML , Anna-Maria Behnsen , Frederic Weisbecker , Stephen Boyd , Peter Zijlstra References: <20241031115448.978498636@linutronix.de> <20241031120328.599430157@linutronix.de> <387b120b-d68a-45e8-b6ab-768cd95d11c2@roeck-us.net> <65b412ef-fc57-4988-bf92-3c924a1c74a5@roeck-us.net> <87cyifxvgj.ffs@tglx> Content-Language: en-US From: Guenter Roeck Autocrypt: addr=linux@roeck-us.net; keydata= xsFNBE6H1WcBEACu6jIcw5kZ5dGeJ7E7B2uweQR/4FGxH10/H1O1+ApmcQ9i87XdZQiB9cpN RYHA7RCEK2dh6dDccykQk3bC90xXMPg+O3R+C/SkwcnUak1UZaeK/SwQbq/t0tkMzYDRxfJ7 nyFiKxUehbNF3r9qlJgPqONwX5vJy4/GvDHdddSCxV41P/ejsZ8PykxyJs98UWhF54tGRWFl 7i1xvaDB9lN5WTLRKSO7wICuLiSz5WZHXMkyF4d+/O5ll7yz/o/JxK5vO/sduYDIlFTvBZDh gzaEtNf5tQjsjG4io8E0Yq0ViobLkS2RTNZT8ICq/Jmvl0SpbHRvYwa2DhNsK0YjHFQBB0FX IdhdUEzNefcNcYvqigJpdICoP2e4yJSyflHFO4dr0OrdnGLe1Zi/8Xo/2+M1dSSEt196rXaC kwu2KgIgmkRBb3cp2vIBBIIowU8W3qC1+w+RdMUrZxKGWJ3juwcgveJlzMpMZNyM1jobSXZ0 VHGMNJ3MwXlrEFPXaYJgibcg6brM6wGfX/LBvc/haWw4yO24lT5eitm4UBdIy9pKkKmHHh7s jfZJkB5fWKVdoCv/omy6UyH6ykLOPFugl+hVL2Prf8xrXuZe1CMS7ID9Lc8FaL1ROIN/W8Vk BIsJMaWOhks//7d92Uf3EArDlDShwR2+D+AMon8NULuLBHiEUQARAQABzTJHdWVudGVyIFJv ZWNrIChMaW51eCBhY2NvdW50KSA8bGludXhAcm9lY2stdXMubmV0PsLBgQQTAQIAKwIbAwYL CQgHAwIGFQgCCQoLBBYCAwECHgECF4ACGQEFAlVcphcFCRmg06EACgkQyx8mb86fmYFg0RAA nzXJzuPkLJaOmSIzPAqqnutACchT/meCOgMEpS5oLf6xn5ySZkl23OxuhpMZTVX+49c9pvBx hpvl5bCWFu5qC1jC2eWRYU+aZZE4sxMaAGeWenQJsiG9lP8wkfCJP3ockNu0ZXXAXwIbY1O1 c+l11zQkZw89zNgWgKobKzrDMBFOYtAh0pAInZ9TSn7oA4Ctejouo5wUugmk8MrDtUVXmEA9 7f9fgKYSwl/H7dfKKsS1bDOpyJlqhEAH94BHJdK/b1tzwJCFAXFhMlmlbYEk8kWjcxQgDWMu GAthQzSuAyhqyZwFcOlMCNbAcTSQawSo3B9yM9mHJne5RrAbVz4TWLnEaX8gA5xK3uCNCeyI sqYuzA4OzcMwnnTASvzsGZoYHTFP3DQwf2nzxD6yBGCfwNGIYfS0i8YN8XcBgEcDFMWpOQhT Pu3HeztMnF3HXrc0t7e5rDW9zCh3k2PA6D2NV4fews9KDFhLlTfCVzf0PS1dRVVWM+4jVl6l HRIAgWp+2/f8dx5vPc4Ycp4IsZN0l1h9uT7qm1KTwz+sSl1zOqKD/BpfGNZfLRRxrXthvvY8 BltcuZ4+PGFTcRkMytUbMDFMF9Cjd2W9dXD35PEtvj8wnEyzIos8bbgtLrGTv/SYhmPpahJA l8hPhYvmAvpOmusUUyB30StsHIU2LLccUPPOwU0ETofVZwEQALlLbQeBDTDbwQYrj0gbx3bq 7kpKABxN2MqeuqGr02DpS9883d/t7ontxasXoEz2GTioevvRmllJlPQERVxM8gQoNg22twF7 pB/zsrIjxkE9heE4wYfN1AyzT+AxgYN6f8hVQ7Nrc9XgZZe+8IkuW/Nf64KzNJXnSH4u6nJM J2+Dt274YoFcXR1nG76Q259mKwzbCukKbd6piL+VsT/qBrLhZe9Ivbjq5WMdkQKnP7gYKCAi pNVJC4enWfivZsYupMd9qn7Uv/oCZDYoBTdMSBUblaLMwlcjnPpOYK5rfHvC4opxl+P/Vzyz 6WC2TLkPtKvYvXmdsI6rnEI4Uucg0Au/Ulg7aqqKhzGPIbVaL+U0Wk82nz6hz+WP2ggTrY1w ZlPlRt8WM9w6WfLf2j+PuGklj37m+KvaOEfLsF1v464dSpy1tQVHhhp8LFTxh/6RWkRIR2uF I4v3Xu/k5D0LhaZHpQ4C+xKsQxpTGuYh2tnRaRL14YMW1dlI3HfeB2gj7Yc8XdHh9vkpPyuT nY/ZsFbnvBtiw7GchKKri2gDhRb2QNNDyBnQn5mRFw7CyuFclAksOdV/sdpQnYlYcRQWOUGY HhQ5eqTRZjm9z+qQe/T0HQpmiPTqQcIaG/edgKVTUjITfA7AJMKLQHgp04Vylb+G6jocnQQX JqvvP09whbqrABEBAAHCwWUEGAECAA8CGwwFAlVcpi8FCRmg08MACgkQyx8mb86fmYHNRQ/+ J0OZsBYP4leJvQF8lx9zif+v4ZY/6C9tTcUv/KNAE5leyrD4IKbnV4PnbrVhjq861it/zRQW cFpWQszZyWRwNPWUUz7ejmm9lAwPbr8xWT4qMSA43VKQ7ZCeTQJ4TC8kjqtcbw41SjkjrcTG wF52zFO4bOWyovVAPncvV9eGA/vtnd3xEZXQiSt91kBSqK28yjxAqK/c3G6i7IX2rg6pzgqh hiH3/1qM2M/LSuqAv0Rwrt/k+pZXE+B4Ud42hwmMr0TfhNxG+X7YKvjKC+SjPjqp0CaztQ0H nsDLSLElVROxCd9m8CAUuHplgmR3seYCOrT4jriMFBtKNPtj2EE4DNV4s7k0Zy+6iRQ8G8ng QjsSqYJx8iAR8JRB7Gm2rQOMv8lSRdjva++GT0VLXtHULdlzg8VjDnFZ3lfz5PWEOeIMk7Rj trjv82EZtrhLuLjHRCaG50OOm0hwPSk1J64R8O3HjSLdertmw7eyAYOo4RuWJguYMg5DRnBk WkRwrSuCn7UG+qVWZeKEsFKFOkynOs3pVbcbq1pxbhk3TRWCGRU5JolI4ohy/7JV1TVbjiDI HP/aVnm6NC8of26P40Pg8EdAhajZnHHjA7FrJXsy3cyIGqvg9os4rNkUWmrCfLLsZDHD8FnU mDW4+i+XlNFUPUYMrIKi9joBhu18ssf5i5Q= In-Reply-To: <87cyifxvgj.ffs@tglx> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 11/28/24 06:51, Thomas Gleixner wrote: > On Wed, Nov 27 2024 at 15:02, Guenter Roeck wrote: >> On 11/27/24 14:08, John Stultz wrote: >> An example log is at [1]. It says >> >> clocksource: npcm7xx-timer1: mask: 0xffffff max_cycles: 0xffffff, max_idle_ns: 597268854 ns > > That's a 24bit counter. So negative motion happens when the readouts are > more than (1 << 23) apart. AFAICT the counter runs with about 14MHz, but > I'd like to have that confirmed. > >> clocksource: jiffies: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 19112604462750000 ns >> ... >> clocksource: Switched to clocksource npcm7xx-timer1 >> >> I don't know where exactly it stalls; sometime after handover to userspace. >> I'll be happy to do some more debugging, but you'll nee to let me know what >> to look for. > > On that platform max_idle_ns should correspond to 50% of the counter > width. So if both CPUs go deep idle for max_idle_ns, then the next timer > interrupt doing the timeeeping advancement sees a delta of > (1 << 23) > and timekeeping stalls. > > If my ssumption is correct, then the below should fix it. > Unfortunately not, it just makes things worse and stalls earlier. [ 2.080000] Fusion MPT SAS Host driver 3.04.20 [ 2.080000] npcm7xx-ehci f0806000.usb: EHCI Host Controller [ 2.080000] npcm7xx-ehci f0806000.usb: new USB bus registered, assigned bus number 1 [ 2.080000] npcm7xx-ehci f0806000.usb: irq 39, io mem 0xf0806000 qemu-system-arm: terminating on signal 15 from pid 17184 (/bin/bash) There is something else going on. I reverted the offending patch and added + pr_warn("###### now: %llx last: %llx mask: %llx return: %llx", now, last, mask, (now - last) & mask); into clocksource_delta(). Here is what I get: ... [ 3.310000] ###### now: f8c502 last: f6c964 mask: ffffff return: 1fb9e [ 3.320000] ###### now: fbc513 last: f8b1ac mask: ffffff return: 31367 [ 3.330000] ###### now: fd368d last: fa99f4 mask: ffffff return: 29c99 [ 3.340000] ###### now: ffe8b3 last: fc823c mask: ffffff return: 36677 [ 3.350000] ###### now: 6c4f last: fe6a84 mask: ffffff return: 201cb <--- [ 3.360000] ###### now: 40427 last: 10052cc mask: ffffff return: 3b15b <--- [ 3.370000] ###### now: 43bfe last: 1023b14 mask: ffffff return: 200ea [ 3.380000] ###### now: 6f438 last: 104235c mask: ffffff return: 2d0dc [ 3.390000] ###### now: 8e9a3 last: 1060ba4 mask: ffffff return: 2ddff [ 3.400000] ###### now: ac9d3 last: 107f3ec mask: ffffff return: 2d5e7 [ 3.410000] ###### now: cb9b4 last: 109dc34 mask: ffffff return: 2dd80 [ 3.420000] ###### now: e9ba2 last: 10bc47c mask: ffffff return: 2d726 [ 3.430000] ###### now: 108994 last: 10dacc4 mask: ffffff return: 2dcd0 [ 3.440000] ###### now: 1200a0 last: 10f950c mask: ffffff return: 26b94 [ 3.450000] ###### now: 14c55f last: 1117d54 mask: ffffff return: 3480b [ 3.460000] ###### now: 15d43a last: 113659c mask: ffffff return: 26e9e ... [ 18.100000] ###### now: f8c39f last: ceea990 mask: ffffff return: a1a0f [ 18.290000] ###### now: 1d01af last: cf832f8 mask: ffffff return: 24ceb7 [ 18.500000] ###### now: 45b0a2 last: d1c7050 mask: ffffff return: 294052 [ 19.090000] ###### now: b5ac62 last: d447e38 mask: ffffff return: 712e2a [ 19.110000] ###### now: b9ebc3 last: db506d0 mask: ffffff return: 4e4f3 [ 19.120000] ###### now: bb842f last: db8d760 mask: ffffff return: 2accf [ 19.160000] ###### now: c43f2e last: dbabfa8 mask: ffffff return: 97f86 'last' advances beyond 'mask', and after that the result is always bad. The call to clocksource_delta() is from timekeeping_advance(). Guenter