Re: [REGRESSION][BISECTED] Long boot time with Xen HVM guests during PV spinlock initialization
Juergen Gross <[email protected]>
| Newsgroups | dev.linux.lists.regressions,org.kernel.vger.linux-kernel,org.xenproject.lists.xen-devel |
|---|---|
| Message-ID | <[email protected]> |
Add Thomas Gleixner (author of the patch introducing the regression).
Juergen
On 08.06.26 12:29, Teddy Astie wrote:
> Hello,
>
> In 6.12.5+ kernels on AMD CPUs, we observe abnormally long boot times where the
> guest is struggling on PV spinlock initialization.
>
> This occurs starting with 6.12.5, and also on more recent kernels on Intel
> platforms, but that hasn't been fully investigated at this time (but I assume
> it's a variant of the same issue).
>
> This occurs since a backport of 76031d9 ("clocksource: Make negative motion
> detection more robust").
>
> Some (claude-based) analysis made appears to relate that to the lack of proper
> max_raw_delta in the jiffies clocksource which appears to make the clock fail to
> progress meaningfully.
>
> Here is a raw summary of the analysis
> > We tracked it down to a single stable backport in 6.12.5: commit 1a678f6829a8
> ("clocksource: Make negative motion detection more robust", upstream
> 76031d9536a0). It introduces a max_raw_delta field on struct clocksource but
> never initializes it for the default boot timekeeper (the jiffies clocksource),
> so clocksource_delta() clamps every delta to 0 and CLOCK_MONOTONIC freezes while
> that clocksource is active. On this HVM guest, SMP bring-up runs while the
> jiffies clocksource is still the timekeeper, and the Xen single shot (high
> resolution) tick then advances jiffies far too slowly, so the secondary CPUs
> burn seconds in calibrate_delay().
>
> Teddy
OpenPGP_0xB0DE9DD628BF132F.asc
(application/pgp-keys, 3.6 KB)
-----BEGIN PGP PUBLIC KEY BLOCK----- xsBNBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjri oyspZKOBycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2 kaV2KL9650I1SJvedYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i 1TXkH09XSSI8mEQ/ouNcMvIJNwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/B BLUVbDa4+gmzDC9ezlZkTZG2t14zWPvxXP3FAp2pkW0xqG7/377qptDmrk42GlSK N4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEBAAHNHEp1ZXJnZW4gR3Jvc3Mg PGpnQHBmdXBmLm5ldD7CwHkEEwECACMFAlOMcBYCGwMHCwkIBwMCAQYVCAIJCgsE FgIDAQIeAQIXgAAKCRCw3p3WKL8TL0KdB/93FcIZ3GCNwFU0u3EjNbNjmXBKDY4F UGNQH2lvWAUy+dnyThpwdtF/jQ6j9RwE8VP0+NXcYpGJDWlNb9/JmYqLiX2Q3Tye vpB0CA3dbBQp0OW0fgCetToGIQrg0MbD1C/sEOv8Mr4NAfbauXjZlvTj30H2jO0u +6WGM6nHwbh2l5O8ZiHkH32iaSTfN7Eu5RnNVUJbvoPHZ8SlM4KWm8rG+lIkGurq qu5gu8q8ZMKdsdGC4bBxdQKDKHEFExLJK/nRPFmAuGlId1E3fe10v5QL+qHI3EIP tyfE7i9Hz6rVwi7lWKgh7pe0ZvatAudZ+JNIlBKptb64FaiIOAWDCx1SzR9KdWVy Z2VuIEdyb3NzIDxqZ3Jvc3NAc3VzZS5jb20+wsB5BBMBAgAjBQJTjHCvAhsDBwsJ CAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/Ey/HmQf/RtI7kv5A2PS4 RF7HoZhPVPogNVbC4YA6lW7DrWf0teC0RR3MzXfy6pJ+7KLgkqMlrAbN/8Dvjoz7 8X+5vhH/rDLa9BuZQlhFmvcGtCF8eR0T1v0nC/nuAFVGy+67q2DH8As3KPu0344T BDpAvr2uYM4tSqxK4DURx5INz4ZZ0WNFHcqsfvlGJALDeE0LhITTd9jLzdDad1pQ SToCnLl6SBJZjDOX9QQcyUigZFtCXFst4dlsvddrxyqT1f17+2cFSdu7+ynLmXBK 7abQ3rwJY8SbRO2iRulogc5vr/RLMMlscDAiDkaFQWLoqHHOdfO9rURssHNN8WkM nQfvUewRz80hSnVlcmdlbiBHcm9zcyA8amdyb3NzQG5vdmVsbC5jb20+wsB5BBMB AgAjBQJTjHDXAhsDBwsJCAcDAgEGFQgCCQoLBBYCAwECHgECF4AACgkQsN6d1ii/ Ey8PUQf/ehmgCI9jB9hlgexLvgOtf7PJnFOXgMLdBQgBlVPO3/D9R8LtF9DBAFPN hlrsfIG/SqICoRCqUcJ96Pn3P7UUinFG/I0ECGF4EvTE1jnDkfJZr6jrbjgyoZHi w/4BNwSTL9rWASyLgqlA8u1mf+c2yUwcGhgkRAd1gOwungxcwzwqgljf0N51N5Jf VRHRtyfwq/ge+YEkDGcTU6Y0sPOuj4Dyfm8fJzdfHNQsWq3PnczLVELStJNdapwP OoE+lotufe3AM2vAEYJ9rTz3Cki4JFUsgLkHFqGZarrPGi1eyQcXeluldO3m91NK /1xMI3/+8jbO0tsn1tqSEUGIJi7ox80eSnVlcmdlbiBHcm9zcyA8amdyb3NzQHN1 c2UuZGU+wsB5BBMBAgAjBQJTjHDrAhsDBwsJCAcDAgEGFQgCCQoLBBYCAwECHgEC F4AACgkQsN6d1ii/Ey+LhQf9GL45eU5vOowA2u5N3g3OZUEBmDHVVbqMtzwlmNC4 k9Kx39r5s2vcFl4tXqW7g9/ViXYuiDXb0RfUpZiIUW89siKrkzmQ5dM7wRqzgJpJ wK8Bn2MIxAKArekWpiCKvBOB/Cc+3EXE78XdlxLyOi/NrmSGRIov0karw2RzMNOu 5D+jLRZQd1Sv27AR+IP3I8U4aqnhLpwhK7MEy9oCILlgZ1QZe49kpcumcZKORmzB TNh30FVKK1EvmV2xAKDoaEOgQB4iFQLhJCdP1I5aSgM5IVFdn7v5YgEYuJYx37Io N1EblHI//x/e2AaIHpzK5h88NEawQsaNRpNSrcfbFmAg987ATQRTjHAWAQgAyzH6 AOODMBjgfWE9VeCgsrwH3exNAU32gLq2xvjpWnHIs98ndPUDpnoxWQugJ6MpMncr 0xSwFmHEgnSEjK/PAjppgmyc57BwKII3sV4on+gDVFJR6Y8ZRwgnBC5mVM6JjQ5x Dk8WRXljExRfUX9pNhdE5eBOZJrDRoLUmmjDtKzWaDhIg/+1Hzz93X4fCQkNVbVF LELU9bMaLPBG/x5q4iYZ2k2ex6d47YE1ZFdMm6YBYMOljGkZKwYde5ldM9mo45mm we0icXKLkpEdIXKTZeKDO+Hdv1aqFuAcccTg9RXDQjmwhC3yEmrmcfl0+rPghO0I v3OOImwTEe4co3c1mwARAQABwsBfBBgBAgAJBQJTjHAWAhsMAAoJELDendYovxMv Q/gH/1ha96vm4P/L+bQpJwrZ/dneZcmEwTbe8YFsw2V/Buv6Z4Mysln3nQK5ZadD 534CF7TDVft7fC4tU4PONxF5D+/tvgkPfDAfF77zy2AH1vJzQ1fOU8lYFpZXTXIH b+559UqvIB8AdgR3SAJGHHt4RKA0F7f5ipYBBrC6cyXJyyoprT10EMvU8VGiwXvT yJz3fjoYsdFzpWPlJEBRMedCot60g5dmbdrZ5DWClAr0yau47zpWj3enf1tLWaqc suylWsviuGjKGw7KHQd3bxALOknAp4dN3QwBYCKuZ7AddY9yjynVaD5X7nF9nO5B jR/i1DG86lem3iBDXzXsZDn8R3/CwO0EGAEIACAWIQSFEmdy6PYElKXQl/ew3p3W KL8TLwUCWt3w0AIbAgCBCRCw3p3WKL8TL3YgBBkWCAAdFiEEUy2wekH2OPMeOLge gFxhu0/YY74FAlrd8NAACgkQgFxhu0/YY75NiwD/fQf/RXpyv9ZX4n8UJrKDq422 bcwkujisT6jix2mOOwYBAKiip9+mAD6W5NPXdhk1XraECcIspcf2ff5kCAlG0DIN aTUH/RIwNWzXDG58yQoLdD/UPcFgi8GWtNUp0Fhc/GeBxGipXYnvuWxwS+Qs1Qay 7/Nbal/v4/eZZaWs8wl2VtrHTS96/IF6q2o0qMey0dq2AxnZbQIULiEndgR625EF RFg+IbO4ldSkB3trsF2ypYLij4ZObm2casLIP7iB8NKmQ5PndL8Y07TtiQ+Sb/wn g4GgV+BJoKdDWLPCAlCMilwbZ88Ijb+HF/aipc9hsqvW/hnXC2GajJSAY3Qs9Mib 4Hm91jzbAjmp7243pQ4bJMfYHemFFBRaoLC7ayqQjcsttN2ufINlqLFPZPR/i3IX kt+z4drzFUyEjLM1vVvIMjkUoJs= =eeAB -----END PGP PUBLIC KEY BLOCK-----
OpenPGP_signature.asc
(application/pgp-signature, 495 B)
-----BEGIN PGP SIGNATURE----- wsB5BAABCAAjFiEEhRJncuj2BJSl0Jf3sN6d1ii/Ey8FAmomoCoFAwAAAAAACgkQsN6d1ii/Ey8y 6wf+OG96gAV1ZcRnq8/dlt9Jje0fZQEXvS3qKFdnHSXZuE7J2l/hCL8Mmsu/0zrLOofq+OqzH/5P eVcZU7/To0S7vr/W21V7u2DooWhAX7jdKtZzcaTY8KMFhnay6ySi7CakSgD8IOEaqbgAfjD2rRfs cIe5jvQ5IarH+wtyEM0tb47YaOB8YI1KaAFbcvHlAaDxMVp2NyeN7NbwC1/y+4TJmLrKX4MqoSiB Mj47/Em8mkKhPI5bCvVoxR1qy0lzcRWx/9oUNtVMYdOdiBDzh9ZMOBgSb+lvSuHlleVSWhUZJu4J It+jwYi9R1vftcBufTT8sPGJhzYgyuvp7IFS+pHBhQ== =h4Ky -----END PGP SIGNATURE-----