[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Xen-users] Xen Clocksource, the VDSO)... not how, but why... and some micro-benchmarks.
- To: Hans van Kranenburg <Hans.van.Kranenburg@xxxxxxxxxx>, "xen-users@xxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxx>
- From: Juergen Gross <jgross@xxxxxxxx>
- Date: Thu, 14 Mar 2019 09:32:10 +0100
- Autocrypt: addr=jgross@xxxxxxxx; prefer-encrypt=mutual; keydata= mQENBFOMcBYBCACgGjqjoGvbEouQZw/ToiBg9W98AlM2QHV+iNHsEs7kxWhKMjrioyspZKOB ycWxw3ie3j9uvg9EOB3aN4xiTv4qbnGiTr3oJhkB1gsb6ToJQZ8uxGq2kaV2KL9650I1SJve dYm8Of8Zd621lSmoKOwlNClALZNew72NjJLEzTalU1OdT7/i1TXkH09XSSI8mEQ/ouNcMvIJ NwQpd369y9bfIhWUiVXEK7MlRgUG6MvIj6Y3Am/BBLUVbDa4+gmzDC9ezlZkTZG2t14zWPvx XP3FAp2pkW0xqG7/377qptDmrk42GlSKN4z76ELnLxussxc7I2hx18NUcbP8+uty4bMxABEB AAG0H0p1ZXJnZW4gR3Jvc3MgPGpncm9zc0BzdXNlLmNvbT6JATkEEwECACMFAlOMcK8CGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRCw3p3WKL8TL8eZB/9G0juS/kDY9LhEXseh mE9U+iA1VsLhgDqVbsOtZ/S14LRFHczNd/Lqkn7souCSoyWsBs3/wO+OjPvxf7m+Ef+sMtr0 G5lCWEWa9wa0IXx5HRPW/ScL+e4AVUbL7rurYMfwCzco+7TfjhMEOkC+va5gzi1KrErgNRHH kg3PhlnRY0Udyqx++UYkAsN4TQuEhNN32MvN0Np3WlBJOgKcuXpIElmMM5f1BBzJSKBkW0Jc Wy3h2Wy912vHKpPV/Xv7ZwVJ27v7KcuZcErtptDevAljxJtE7aJG6WiBzm+v9EswyWxwMCIO RoVBYuiocc51872tRGywc03xaQydB+9R7BHPuQENBFOMcBYBCADLMfoA44MwGOB9YT1V4KCy vAfd7E0BTfaAurbG+Olacciz3yd09QOmejFZC6AnoykydyvTFLAWYcSCdISMr88COmmCbJzn sHAogjexXiif6ANUUlHpjxlHCCcELmZUzomNDnEOTxZFeWMTFF9Rf2k2F0Tl4E5kmsNGgtSa aMO0rNZoOEiD/7UfPP3dfh8JCQ1VtUUsQtT1sxos8Eb/HmriJhnaTZ7Hp3jtgTVkV0ybpgFg w6WMaRkrBh17mV0z2ajjmabB7SJxcouSkR0hcpNl4oM74d2/VqoW4BxxxOD1FcNCObCELfIS auZx+XT6s+CE7Qi/c44ibBMR7hyjdzWbABEBAAGJAR8EGAECAAkFAlOMcBYCGwwACgkQsN6d 1ii/Ey9D+Af/WFr3q+bg/8v5tCknCtn92d5lyYTBNt7xgWzDZX8G6/pngzKyWfedArllp0Pn fgIXtMNV+3t8Li1Tg843EXkP7+2+CQ98MB8XvvPLYAfW8nNDV85TyVgWlldNcgdv7nn1Sq8g HwB2BHdIAkYce3hEoDQXt/mKlgEGsLpzJcnLKimtPXQQy9TxUaLBe9PInPd+Ohix0XOlY+Uk QFEx50Ki3rSDl2Zt2tnkNYKUCvTJq7jvOlaPd6d/W0tZqpyy7KVay+K4aMobDsodB3dvEAs6 ScCnh03dDAFgIq5nsB11j3KPKdVoPlfucX2c7kGNH+LUMbzqV6beIENfNexkOfxHf4kBrQQY AQgAIBYhBIUSZ3Lo9gSUpdCX97DendYovxMvBQJa3fDQAhsCAIEJELDendYovxMvdiAEGRYI AB0WIQRTLbB6QfY48x44uB6AXGG7T9hjvgUCWt3w0AAKCRCAXGG7T9hjvk2LAP99B/9FenK/ 1lfifxQmsoOrjbZtzCS6OKxPqOLHaY47BgEAqKKn36YAPpbk09d2GTVetoQJwiylx/Z9/mQI CUbQMg1pNQf9EjA1bNcMbnzJCgt0P9Q9wWCLwZa01SnQWFz8Z4HEaKldie+5bHBL5CzVBrLv 81tqX+/j95llpazzCXZW2sdNL3r8gXqrajSox7LR2rYDGdltAhQuISd2BHrbkQVEWD4hs7iV 1KQHe2uwXbKlguKPhk5ubZxqwsg/uIHw0qZDk+d0vxjTtO2JD5Jv/CeDgaBX4Emgp0NYs8IC UIyKXBtnzwiNv4cX9qKlz2Gyq9b+GdcLYZqMlIBjdCz0yJvgeb3WPNsCOanvbjelDhskx9gd 6YUUFFqgsLtrKpCNyy203a58g2WosU9k9H+LcheS37Ph2vMVTISMszW9W8gyORSgmw==
- Delivery-date: Thu, 14 Mar 2019 08:33:22 +0000
- List-id: Xen user discussion <xen-users.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 11/03/2019 01:05, Hans van Kranenburg wrote:
> On 3/7/19 5:39 PM, Hans van Kranenburg wrote:
>> [...]
>>
>> I still haven't found the exact reason why we should add clocksource=tsc
>> tsc=stable:socket to the hypervisor command line. It's not needed to
>> make all tsc vdso trickery in the domU work. Moreover, it does not even
>> seem needed at all to set clocksource=tsc in xen to be able to use it in
>> the domU?
>>
>> The only place where I can find tsc=stable:socket being mentioned is
>> https://lore.kernel.org/patchwork/cover/849340/ which should be a
>> changeset to enable vdso calls for the xen clocksource (in linux 4.15).
>> But that never got merged.
>
> Well, I went on a journey to find out what tsc=stable:socket is actually
> doing, and that journey ended rather soon. :D
>
> The tsc=stable:socket was introduced in...
>
> commit bc900cbc8f37b93cc6c9f6370beb14e6430b334d
> Author: Joao Martins <joao.m.martins@xxxxxxxxxx>
> Date: Fri Sep 23 18:26:19 2016 +0200
>
> x86/time: extend "tsc" param with "stable:socket"
>
> ...and nothing at all seems to be using TSC_RELIABLE_SOCKET or the
> tsc_flags introduced there in the code further on.
>
> +/* TSC is reliable across sockets */
> +#define TSC_RELIABLE_SOCKET (1 << 0)
>
> So, that command line part is effectively a noop. Maybe it was added
> because that linux patchset for xen clocksource wanted to use it? But,
> those patches also don't explain what would be special about this extra
> option and what it would be used for.
>
What about its usage in init_tsc()? It will clearly have an effect on
systems with multiple sockets.
Juergen
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-users
|
