Re: [Xen-devel] [RFC PATCH v3 1/2] xen: credit2: enable per cpu runqueue creation

[Dario Faggioli]

Hello Praveen,

On Fri, 2017-03-31 at 00:58 +0530, Praveen Kumar wrote:
> The patch introduces a new command line option 'cpu' that when used
> will
> create runqueue per logical pCPU.
> 
I'd add a quick note about why we think it's a good idea to have this.
Something like:

"This may be useful for small systems, and also for development,
performance evaluation and comparison."

> Signed-off-by: Praveen Kumar 
>
With that addition, at least this patch can have my:

Reviewed-by: Dario Faggioli 

Thanks and Regards,
Dario
-- 
<> (Raistlin Majere)
-
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R Ltd., Cambridge (UK)

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[Xen-devel] [RFC PATCH v3 1/2] xen: credit2: enable per cpu runqueue creation

[Praveen Kumar]

The patch introduces a new command line option 'cpu' that when used will
create runqueue per logical pCPU.

Signed-off-by: Praveen Kumar 
---
 docs/misc/xen-command-line.markdown |  3 ++-
 xen/common/sched_credit2.c  | 15 +++
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/docs/misc/xen-command-line.markdown 
b/docs/misc/xen-command-line.markdown
index 9eb85d68b5..c245cfa471 100644
--- a/docs/misc/xen-command-line.markdown
+++ b/docs/misc/xen-command-line.markdown
@@ -525,7 +525,7 @@ also slow in responding to load changes.
 The default value of `1 sec` is rather long.
 
 ### credit2\_runqueue
-> `= core | socket | node | all`
+> `= cpu | core | socket | node | all`
 
 > Default: `socket`
 
@@ -536,6 +536,7 @@ balancing (for instance, it will deal better with 
hyperthreading),
 but also more overhead.
 
 Available alternatives, with their meaning, are:
+* `cpu`: one runqueue per each logical pCPUs of the host;
 * `core`: one runqueue per each physical core of the host;
 * `socket`: one runqueue per each physical socket (which often,
 but not always, matches a NUMA node) of the host;
diff --git a/xen/common/sched_credit2.c b/xen/common/sched_credit2.c
index bb1c657e76..ee7b443f9e 100644
--- a/xen/common/sched_credit2.c
+++ b/xen/common/sched_credit2.c
@@ -301,6 +301,9 @@ integer_param("credit2_balance_over", 
opt_overload_balance_tolerance);
  * want that to happen basing on topology. At the moment, it is possible
  * to choose to arrange runqueues to be:
  *
+ * - per-cpu: meaning that there will be one runqueue per logical cpu. This
+ *will happen when if the opt_runqueue parameter is set to 'cpu'.
+ *
  * - per-core: meaning that there will be one runqueue per each physical
  * core of the host. This will happen if the opt_runqueue
  * parameter is set to 'core';
@@ -322,11 +325,13 @@ integer_param("credit2_balance_over", 
opt_overload_balance_tolerance);
  * either the same physical core, the same physical socket, the same NUMA
  * node, or just all of them, will be put together to form runqueues.
  */
-#define OPT_RUNQUEUE_CORE   0
-#define OPT_RUNQUEUE_SOCKET 1
-#define OPT_RUNQUEUE_NODE   2
-#define OPT_RUNQUEUE_ALL3
+#define OPT_RUNQUEUE_CPU0
+#define OPT_RUNQUEUE_CORE   1
+#define OPT_RUNQUEUE_SOCKET 2
+#define OPT_RUNQUEUE_NODE   3
+#define OPT_RUNQUEUE_ALL4
 static const char *const opt_runqueue_str[] = {
+[OPT_RUNQUEUE_CPU] = "cpu",
 [OPT_RUNQUEUE_CORE] = "core",
 [OPT_RUNQUEUE_SOCKET] = "socket",
 [OPT_RUNQUEUE_NODE] = "node",
@@ -682,6 +687,8 @@ cpu_to_runqueue(struct csched2_private *prv, unsigned int 
cpu)
 BUG_ON(cpu_to_socket(cpu) == XEN_INVALID_SOCKET_ID ||
cpu_to_socket(peer_cpu) == XEN_INVALID_SOCKET_ID);
 
+if (opt_runqueue == OPT_RUNQUEUE_CPU)
+continue;
 if ( opt_runqueue == OPT_RUNQUEUE_ALL ||
  (opt_runqueue == OPT_RUNQUEUE_CORE && same_core(peer_cpu, cpu)) ||
  (opt_runqueue == OPT_RUNQUEUE_SOCKET && same_socket(peer_cpu, 
cpu)) ||
-- 
2.12.0


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