By: Linus Torvalds (torvalds.delete@this.linux-foundation.org), August 21, 2018 5:13 pm
Room: Moderated Discussions
Travis (travis.downs.delete@this.gmail.com) on August 21, 2018 4:59 pm wrote:
>
> Sure, but the crazy stuff was for people who wanted to move down an order of magnitude
> in cost and avoid the atomic cost: the goal is like 1,2 or 3 cycles, not 15 or 20. Then
> the problem is that reading the CPU number is the slowest part of the whole thing.
Yes, and this is what rseq solves. The cpu number is right there in the rseq data structure, so you can use it directly.
But yes, you have to be pretty serious about your statistics scaling for this to make sense. And you'll have to have whatever non-rseq fallback for older kernel versions and other OS's. So it's still not wonderful, but it's exactly the kind of thing rseq was designed for.
Linus
>
> Sure, but the crazy stuff was for people who wanted to move down an order of magnitude
> in cost and avoid the atomic cost: the goal is like 1,2 or 3 cycles, not 15 or 20. Then
> the problem is that reading the CPU number is the slowest part of the whole thing.
Yes, and this is what rseq solves. The cpu number is right there in the rseq data structure, so you can use it directly.
But yes, you have to be pretty serious about your statistics scaling for this to make sense. And you'll have to have whatever non-rseq fallback for older kernel versions and other OS's. So it's still not wonderful, but it's exactly the kind of thing rseq was designed for.
Linus
| Topic | Posted By | Date |
|---|---|---|
| ARM turns to a god and a hero | AM | 2018/08/16 09:32 AM |
| ARM turns to a god and a hero | Maynard Handley | 2018/08/16 09:41 AM |
| ARM turns to a god and a hero | Doug S | 2018/08/16 11:11 AM |
| ARM turns to a god and a hero | Geoff Langdale | 2018/08/16 11:59 PM |
| ARM turns to a god and a hero | dmcq | 2018/08/17 05:12 AM |
| ARM is somewhat misleading | Adrian | 2018/08/16 11:56 PM |
| It's marketing material | Gabriele Svelto | 2018/08/17 01:00 AM |
| It's marketing material | Michael S | 2018/08/17 03:13 AM |
| It's marketing material | dmcq | 2018/08/17 05:23 AM |
| It's marketing material | Andrei Frumusanu | 2018/08/17 07:25 AM |
| It's marketing material | Linus Torvalds | 2018/08/17 11:20 AM |
| It's marketing material | Groo | 2018/08/17 01:44 PM |
| It's marketing material | Doug S | 2018/08/17 02:14 PM |
| promises and deliveries | AM | 2018/08/17 02:32 PM |
| promises and deliveries | Passing Through | 2018/08/17 03:02 PM |
| Just by way of clarification | Passing Through | 2018/08/17 03:15 PM |
| Just by way of clarification | AM | 2018/08/18 12:49 PM |
| Just by way of clarification | Passing Through | 2018/08/18 01:34 PM |
| This ain't the nineties any longer | Passing Through | 2018/08/18 01:54 PM |
| This ain't the nineties any longer | Maynard Handley | 2018/08/18 02:50 PM |
| This ain't the nineties any longer | Passing Through | 2018/08/18 03:57 PM |
| This ain't the nineties any longer | Passing Through | 2018/09/06 02:42 PM |
| This ain't the nineties any longer | Maynard Handley | 2018/09/07 04:10 PM |
| This ain't the nineties any longer | Passing Through | 2018/09/07 04:48 PM |
| This ain't the nineties any longer | Maynard Handley | 2018/09/07 05:22 PM |
| Just by way of clarification | Wilco | 2018/08/18 01:26 PM |
| Just by way of clarification | Passing Through | 2018/08/18 01:39 PM |
| Just by way of clarification | none | 2018/08/18 10:52 PM |
| Just by way of clarification | dmcq | 2018/08/19 08:32 AM |
| Just by way of clarification | none | 2018/08/19 08:54 AM |
| Just by way of clarification | dmcq | 2018/08/19 11:24 AM |
| Just by way of clarification | none | 2018/08/19 11:52 AM |
| Just by way of clarification | Gabriele Svelto | 2018/08/19 06:41 AM |
| Just by way of clarification | Passing Through | 2018/08/19 09:25 AM |
| Whiteboards at Gatwick airport anyone? | Passing Through | 2018/08/20 04:24 AM |
| It's marketing material | Michael S | 2018/08/18 11:12 AM |
| It's marketing material | Brett | 2018/08/18 05:22 PM |
| It's marketing material | Brett | 2018/08/18 05:33 PM |
| It's marketing material | Adrian | 2018/08/19 01:21 AM |
| A76 | AM | 2018/08/17 02:45 PM |
| A76 | Michael S | 2018/08/18 11:20 AM |
| A76 | AM | 2018/08/18 12:39 PM |
| A76 | Michael S | 2018/08/18 12:49 PM |
| A76 | AM | 2018/08/18 01:06 PM |
| A76 | Doug S | 2018/08/18 01:43 PM |
| A76 | Maynard Handley | 2018/08/18 02:42 PM |
| A76 | Maynard Handley | 2018/08/18 04:22 PM |
| Why write zeros when one can use metadata? | Paul A. Clayton | 2018/08/18 06:19 PM |
| Why write zeros when one can use metadata? | Maynard Handley | 2018/08/19 11:12 AM |
| Dictionary compress might apply to memcopy | Paul A. Clayton | 2018/08/19 01:45 PM |
| Instructions for zeroing | Konrad Schwarz | 2018/08/30 06:37 AM |
| Instructions for zeroing | Maynard Handley | 2018/08/30 08:41 AM |
| Instructions for zeroing | Adrian | 2018/08/30 11:37 AM |
| dcbz -> dcbzl (was: Instructions for zeroing) | hobold | 2018/08/31 01:50 AM |
| dcbz -> dcbzl (was: Instructions for zeroing) | dmcq | 2018/09/01 05:28 AM |
| A76 | Travis | 2018/08/19 11:36 AM |
| A76 | Maynard Handley | 2018/08/19 12:22 PM |
| A76 | Travis | 2018/08/19 02:07 PM |
| A76 | Maynard Handley | 2018/08/19 06:24 PM |
| Remote atomics | matthew | 2018/08/19 12:51 PM |
| Remote atomics | Michael S | 2018/08/19 01:58 PM |
| Remote atomics | matthew | 2018/08/19 02:32 PM |
| Remote atomics | Michael S | 2018/08/19 02:36 PM |
| Remote atomics | matthew | 2018/08/19 02:48 PM |
| Remote atomics | Michael S | 2018/08/19 03:16 PM |
| Remote atomics | Ricardo B | 2018/08/20 10:05 AM |
| Remote atomics | dmcq | 2018/08/19 02:33 PM |
| Remote atomics | Travis | 2018/08/19 02:32 PM |
| Remote atomics | Michael S | 2018/08/19 02:46 PM |
| Remote atomics | Travis | 2018/08/19 05:35 PM |
| Remote atomics | Michael S | 2018/08/20 03:29 AM |
| Remote atomics | matthew | 2018/08/19 07:58 PM |
| Remote atomics | anon | 2018/08/20 12:59 AM |
| Remote atomics | Travis | 2018/08/20 10:26 AM |
| Remote atomics | Travis | 2018/08/20 09:57 AM |
| Remote atomics | Linus Torvalds | 2018/08/20 04:29 PM |
| Fitting time slices to execution phases | Paul A. Clayton | 2018/08/21 09:09 AM |
| Fitting time slices to execution phases | Linus Torvalds | 2018/08/21 02:34 PM |
| Fitting time slices to execution phases | Linus Torvalds | 2018/08/21 03:31 PM |
| Fitting time slices to execution phases | Gabriele Svelto | 2018/08/21 03:54 PM |
| Fitting time slices to execution phases | Linus Torvalds | 2018/08/21 04:26 PM |
| Fitting time slices to execution phases | Travis | 2018/08/21 04:21 PM |
| Fitting time slices to execution phases | Linus Torvalds | 2018/08/21 04:39 PM |
| Fitting time slices to execution phases | Travis | 2018/08/21 04:59 PM |
| Fitting time slices to execution phases | Linus Torvalds | 2018/08/21 05:13 PM |
| Fitting time slices to execution phases | anon | 2018/08/21 04:27 PM |
| Fitting time slices to execution phases | Linus Torvalds | 2018/08/21 06:02 PM |
| Fitting time slices to execution phases | Etienne | 2018/08/22 02:28 AM |
| Fitting time slices to execution phases | Gabriele Svelto | 2018/08/22 03:07 PM |
| Fitting time slices to execution phases | Travis | 2018/08/22 04:00 PM |
| Fitting time slices to execution phases | anon | 2018/08/22 06:52 PM |
| Fitting time slices to execution phases | Travis | 2018/08/21 04:37 PM |
| Is preventing misuse that complex? | Paul A. Clayton | 2018/08/23 05:42 AM |
| Is preventing misuse that complex? | Linus Torvalds | 2018/08/23 12:46 PM |
| Is preventing misuse that complex? | Travis | 2018/08/23 01:29 PM |
| Is preventing misuse that complex? | Travis | 2018/08/23 01:33 PM |
| Is preventing misuse that complex? | Jeff S. | 2018/08/24 07:57 AM |
| Is preventing misuse that complex? | Travis | 2018/08/24 08:47 AM |
| Is preventing misuse that complex? | Linus Torvalds | 2018/08/23 02:30 PM |
| Is preventing misuse that complex? | Travis | 2018/08/23 03:11 PM |
| Is preventing misuse that complex? | Linus Torvalds | 2018/08/24 01:00 PM |
| Is preventing misuse that complex? | Gabriele Svelto | 2018/08/24 01:25 PM |
| Is preventing misuse that complex? | Linus Torvalds | 2018/08/24 01:33 PM |
| Fitting time slices to execution phases | Travis | 2018/08/21 03:54 PM |
| rseq: holy grail rwlock? | Travis | 2018/08/21 03:18 PM |
| rseq: holy grail rwlock? | Linus Torvalds | 2018/08/21 03:59 PM |
| rseq: holy grail rwlock? | Travis | 2018/08/21 04:27 PM |
| rseq: holy grail rwlock? | Linus Torvalds | 2018/08/21 05:10 PM |
| rseq: holy grail rwlock? | Travis | 2018/08/21 06:21 PM |
| ARM design houses | Michael S | 2018/08/21 05:07 AM |
| ARM design houses | Wilco | 2018/08/22 12:38 PM |
| ARM design houses | Michael S | 2018/08/22 02:21 PM |
| ARM design houses | Wilco | 2018/08/22 03:23 PM |
| ARM design houses | Michael S | 2018/08/29 01:58 AM |
| Qualcomm's core naming scheme really, really sucks | Heikki Kultala | 2018/08/29 02:19 AM |
| A76 | Maynard Handley | 2018/08/18 02:07 PM |
| A76 | Michael S | 2018/08/18 02:32 PM |
| A76 | Maynard Handley | 2018/08/18 02:52 PM |
| A76 | Michael S | 2018/08/18 03:04 PM |
| ARM is somewhat misleading | juanrga | 2018/08/17 01:20 AM |
| Surprised?? | Alberto | 2018/08/17 01:52 AM |
| Surprised?? | Alberto | 2018/08/17 02:10 AM |
| Surprised?? | none | 2018/08/17 02:46 AM |
| Garbage talk | Andrei Frumusanu | 2018/08/17 07:30 AM |
| Garbage talk | Michael S | 2018/08/17 07:43 AM |
| Garbage talk | Andrei Frumusanu | 2018/08/17 09:51 AM |
| Garbage talk | Michael S | 2018/08/18 11:29 AM |
| Garbage talk | Adrian | 2018/08/17 08:28 AM |
| Garbage talk | Alberto | 2018/08/17 09:20 AM |
| Garbage talk | Andrei Frumusanu | 2018/08/17 09:48 AM |
| Garbage talk | Adrian | 2018/08/17 10:17 AM |
| Garbage talk | Andrei Frumusanu | 2018/08/17 10:36 AM |
| Garbage talk | Adrian | 2018/08/17 02:53 PM |
| Garbage talk | Andrei Frumusanu | 2018/08/18 12:17 AM |
| More like a religion he?? ARM has an easy life :) | Alberto | 2018/08/17 09:13 AM |
| More like a religion he?? ARM has an easy life :) | Andrei Frumusanu | 2018/08/17 09:34 AM |
| More like a religion he?? ARM has an easy life :) | Alberto | 2018/08/17 10:03 AM |
| More like a religion he?? ARM has an easy life :) | Andrei Frumusanu | 2018/08/17 10:43 AM |
| More like a religion he?? ARM has an easy life :) | Doug S | 2018/08/17 02:17 PM |
| 15W phone SoCs | AM | 2018/08/17 03:04 PM |
| More like a religion he?? ARM has an easy life :) | Maynard Handley | 2018/08/17 12:29 PM |
| my future stuff will be better than your old stuff, hey I'm a god at last (NT) | Eric Bron | 2018/08/18 03:34 AM |
| my future stuff will be better than your old stuff, hey I'm a god at last | none | 2018/08/18 08:34 AM |
