From: "Jürgen Groß" <jgross@suse.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Dario Faggioli <dfaggioli@suse.com>,
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: Tue, 1 Dec 2020 10:18:50 +0100 [thread overview]
Message-ID: <a812d9a9-a701-bb58-01bf-9375ad4feb50@suse.com> (raw)
In-Reply-To: <54301d8c-2d69-3206-6c42-d2638b7e7aa3@suse.com>
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On 01.12.20 10:12, Jan Beulich wrote:
> On 01.12.2020 09:21, Juergen Gross wrote:
>> @@ -260,23 +257,42 @@ static struct cpupool *cpupool_create(
>>
>> spin_lock(&cpupool_lock);
>>
>> - for_each_cpupool(q)
>> + if ( poolid != CPUPOOLID_NONE )
>> {
>> - last = (*q)->cpupool_id;
>> - if ( (poolid != CPUPOOLID_NONE) && (last >= poolid) )
>> - break;
>> + q = __cpupool_find_by_id(poolid, false);
>> + if ( !q )
>> + list_add_tail(&c->list, &cpupool_list);
>> + else
>> + {
>> + list_add_tail(&c->list, &q->list);
>> + if ( q->cpupool_id == poolid )
>> + {
>> + *perr = -EEXIST;
>> + goto err;
>> + }
>
> You bail _after_ having added the new entry to the list?
Yes, this is making exit handling easier.
>
>> + }
>> +
>> + c->cpupool_id = poolid;
>> }
>> - if ( *q != NULL )
>> + else
>> {
>> - if ( (*q)->cpupool_id == poolid )
>> + /* Cpupool 0 is created with specified id at boot and never removed. */
>> + ASSERT(!list_empty(&cpupool_list));
>> +
>> + q = list_last_entry(&cpupool_list, struct cpupool, list);
>> + /* In case of wrap search for first free id. */
>> + if ( q->cpupool_id == CPUPOOLID_NONE - 1 )
>> {
>> - *perr = -EEXIST;
>> - goto err;
>> + list_for_each_entry(q, &cpupool_list, list)
>> + if ( q->cpupool_id + 1 != list_next_entry(q, list)->cpupool_id )
>> + break;
>> }
>> - c->next = *q;
>> +
>> + list_add(&c->list, &q->list);
>> +
>> + c->cpupool_id = q->cpupool_id + 1;
>
> 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.
Juergen
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next prev parent reply other threads:[~2020-12-01 9:19 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 [this message]
2020-12-04 16:13 ` Dario Faggioli
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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