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From: Dario Faggioli <dfaggioli@suse.com>
To: "Jürgen Groß" <jgross@suse.com>, "Jan Beulich" <jbeulich@suse.com>
Cc: George Dunlap <george.dunlap@citrix.com>, xen-devel@lists.xenproject.org
Subject: Re: [PATCH v2 05/17] xen/cpupool: switch cpupool list to normal list interface
Date: Fri, 04 Dec 2020 17:13:21 +0100	[thread overview]
Message-ID: <fe0b6924122aa9dff2095403738f111750cc815a.camel@suse.com> (raw)
In-Reply-To: <a812d9a9-a701-bb58-01bf-9375ad4feb50@suse.com>

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On Tue, 2020-12-01 at 10:18 +0100, Jürgen Groß wrote:
> On 01.12.20 10:12, Jan Beulich wrote:
> > What guarantees that you managed to find an unused ID, other
> > than at current CPU speeds it taking too long to create 4
> > billion pools? Since you're doing this under lock, wouldn't
> > it help anyway to have a global helper variable pointing at
> > the lowest pool followed by an unused ID?
> 
> An admin doing that would be quite crazy and wouldn't deserve better.
> 
> For being usable a cpupool needs to have a cpu assigned to it. And I
> don't think we are coming even close to 4 billion supported cpus. :-)
> 
> Yes, it would be possible to create 4 billion empty cpupools, but for
> what purpose? There are simpler ways to make the system unusable with
> dom0 root access.
> 
Yes, I agree. I don't think it's worth going through too much effort
for trying to deal with that.

What I'd do is:
 - add a comment here, explaining quickly exactly this fact, i.e., 
   that it's not that we've forgotten to deal with this and it's all 
   on purpose. Actually, it can be either a comment here or it can be 
   mentioned in the changelog. I'm fine either way
 - if we're concerned about someone doing:
     for i=1...N { xl cpupool-create foo bar }
   with N ending up being some giant number, e.g., by mistake, I don't 
   think it's unreasonable to come up with an high enough (but 
   certainly not in the billions!) MAX_CPUPOOLS, and stop creating new
   ones when we reach that level.

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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<<This happens because _I_ choose it to happen!>> (Raistlin Majere)

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  reply	other threads:[~2020-12-04 16:13 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-01  8:21 [PATCH v2 00/17] xen: support per-cpupool scheduling granularity Juergen Gross
2020-12-01  8:21 ` [PATCH v2 01/17] xen/cpupool: add cpu to sched_res_mask when removing it from cpupool Juergen Gross
2020-12-01  8:21 ` [PATCH v2 02/17] xen/cpupool: add missing bits for per-cpupool scheduling granularity Juergen Gross
2020-12-01  8:21 ` [PATCH v2 03/17] xen/cpupool: sort included headers in cpupool.c Juergen Gross
2020-12-01  8:21 ` [PATCH v2 04/17] xen/cpupool: switch cpupool id to unsigned Juergen Gross
2020-12-01  8:55   ` Jan Beulich
2020-12-01  9:01     ` Jürgen Groß
2020-12-01  9:07       ` Jan Beulich
2020-12-07  9:59       ` Jan Beulich
2020-12-07 14:48         ` Jürgen Groß
2020-12-07 15:00           ` Jan Beulich
2020-12-04 15:52   ` Dario Faggioli
2020-12-07  9:58     ` Jan Beulich
2020-12-07 15:21     ` Jan Beulich
2020-12-01  8:21 ` [PATCH v2 05/17] xen/cpupool: switch cpupool list to normal list interface Juergen Gross
2020-12-01  9:12   ` Jan Beulich
2020-12-01  9:18     ` Jürgen Groß
2020-12-04 16:13       ` Dario Faggioli [this message]
2020-12-04 16:16         ` Jürgen Groß
2020-12-04 16:25           ` Dario Faggioli
2020-12-04 16:56   ` Dario Faggioli
2020-12-01  8:21 ` [PATCH v2 06/17] xen/cpupool: use ERR_PTR() for returning error cause from cpupool_create() Juergen Gross
2020-12-02  8:58   ` Jan Beulich
2020-12-02  9:56     ` Jürgen Groß
2020-12-02 10:46       ` Jan Beulich
2020-12-02 10:58         ` Jürgen Groß
2020-12-04 16:29   ` Dario Faggioli
2020-12-01  8:21 ` [PATCH v2 07/17] xen/cpupool: support moving domain between cpupools with different granularity Juergen Gross
2020-12-01  8:21 ` [PATCH v2 08/17] docs: fix hypfs path documentation Juergen Gross
2020-12-01  8:21 ` [PATCH v2 09/17] xen/hypfs: move per-node function pointers into a dedicated struct Juergen Gross
2020-12-02 15:36   ` Jan Beulich
2020-12-02 15:41     ` Jürgen Groß
2020-12-03  8:47     ` Jürgen Groß
2020-12-03  9:12       ` Jan Beulich
2020-12-03  9:51         ` Jürgen Groß
2020-12-01  8:21 ` [PATCH v2 10/17] xen/hypfs: pass real failure reason up from hypfs_get_entry() Juergen Gross
2020-12-01  8:21 ` [PATCH v2 11/17] xen/hypfs: add getsize() and findentry() callbacks to hypfs_funcs Juergen Gross
2020-12-02 15:42   ` Jan Beulich
2020-12-02 15:51     ` Jürgen Groß
2020-12-03  8:12       ` Jan Beulich
2020-12-03  9:39         ` Jürgen Groß
2020-12-04  8:58   ` Jan Beulich
2020-12-04 11:14     ` Jürgen Groß
2020-12-01  8:21 ` [PATCH v2 12/17] xen/hypfs: add new enter() and exit() per node callbacks Juergen Gross
2020-12-03 14:59   ` Jan Beulich
2020-12-03 15:14     ` Jürgen Groß
2020-12-03 15:29       ` Jan Beulich
2020-12-04  8:33         ` Jürgen Groß
2020-12-04  8:30   ` Jan Beulich
2020-12-04  8:35     ` Jürgen Groß
2020-12-01  8:21 ` [PATCH v2 13/17] xen/hypfs: support dynamic hypfs nodes Juergen Gross
2020-12-03 15:08   ` Jan Beulich
2020-12-03 15:18     ` Jürgen Groß
2020-12-01  8:21 ` [PATCH v2 14/17] xen/hypfs: add support for id-based dynamic directories Juergen Gross
2020-12-03 15:44   ` Jan Beulich
2020-12-04  8:52     ` Jürgen Groß
2020-12-04  9:16       ` Jan Beulich
2020-12-04 13:08         ` Jürgen Groß
2020-12-07  7:54           ` Jan Beulich
2020-12-01  8:21 ` [PATCH v2 15/17] xen/cpupool: add cpupool directories Juergen Gross
2020-12-01  9:00   ` Jan Beulich
2020-12-01  9:03     ` Jürgen Groß
2020-12-02 15:46   ` Jürgen Groß
2020-12-03 14:46     ` Jan Beulich
2020-12-03 15:11       ` Jürgen Groß
2020-12-04  9:10   ` Jan Beulich
2020-12-04 11:08     ` Jürgen Groß
2020-12-04 11:54       ` Jan Beulich
2020-12-01  8:21 ` [PATCH v2 16/17] xen/cpupool: add scheduling granularity entry to cpupool entries Juergen Gross
2020-12-01  8:21 ` [PATCH v2 17/17] xen/cpupool: make per-cpupool sched-gran hypfs node writable Juergen Gross
2020-12-04 23:53 ` [PATCH v2 00/17] xen: support per-cpupool scheduling granularity Andrew Cooper
2020-12-05  7:41   ` Jürgen Groß
2020-12-07  9:00   ` Jan Beulich

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