Hi,
On 21/03/2022 15:58, Luca Fancellu wrote:
On 18 Mar 2022, at 16:12, Julien Grall <jul...@xen.org> wrote:
Hi Luca,
I only skimmed through the series. I have one question below:
On 18/03/2022 15:25, Luca Fancellu wrote:
+void __init btcpupools_allocate_pools(void)
+{
+ unsigned int i;
+ bool add_extra_cpupool = false;
+
+ /*
+ * If there are no cpupools, the value of next_pool_id is zero, so the code
+ * below will assign every cpu to cpupool0 as the default behavior.
+ * When there are cpupools, the code below is assigning all the not
+ * assigned cpu to a new pool (next_pool_id value is the last id + 1).
+ * In the same loop we check if there is any assigned cpu that is not
+ * online.
+ */
+ for ( i = 0; i < nr_cpu_ids; i++ )
+ if ( cpumask_test_cpu(i, &cpu_online_map) )
+ {
+ /* Unassigned cpu gets next_pool_id pool id value */
+ if ( pool_cpu_map[i] < 0 )
+ {
+ pool_cpu_map[i] = next_pool_id;
+ add_extra_cpupool = true;
+ }
+ printk(XENLOG_INFO "Logical CPU %u in Pool-%u.\n", i,
+ pool_cpu_map[i]);
+ }
+ else
+ {
+ if ( pool_cpu_map[i] >= 0 )
+ panic("Pool-%d contains cpu%u that is not online!\n",
+ pool_cpu_map[i], i);
+ }
+
+ if ( add_extra_cpupool )
+ next_pool_id++;
+
+ /* Create cpupools with selected schedulers */
+ for ( i = 0; i < next_pool_id; i++ )
+ cpupool_create_pool(i, pool_sched_map[i]);
+
+#ifdef CONFIG_X86
+ /* Cpu0 must be in cpupool0 for x86 */
+ if ( pool_cpu_map[0] != 0 )
+ panic("Cpu0 must be in Pool-0\n");
+#endif
Can you document why this is necessary on x86 but not on other architectures?
Hi Julien,
I received the warning by Juergen here:
https://patchwork.kernel.org/comment/24740762/ that at least on x86 there could
be
some problems if cpu0 is not in cpupool0, I tested it on arm and it was working
fine and I didn’t find any restriction.
What exactly did you test on Arm?
So I don’t know why on x86 we must have cpu0 in cpupool0, maybe x86 maintainer
have more knowledge about that and
I can put a comment here.
On Arm, we are not yet supporting all the CPU features that x86 supports
(e.g. CPU hotplug, suspend/resume...). So I a am bit concerned that the
restriction is just not there yet (or possibly hidden).
Therefore, before lifting the restriction on Arm (and other arch), I
would like us to understand why it is necessary on x86.
We may not have the answer quickly, so is it going to be a problem to
keep the restriction on Arm?
Cheers,
--
Julien Grall
