Re: [PATCH] eal: added new `rte_lcore_is_service_lcore` API.

On Mon, Aug 28, 2017 at 03:24:06PM +0000, Van Haaren, Harry wrote:

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-----Original Message-----
From: Pavan Nikhilesh Bhagavatula [mailto:pbhagavatula@caviumnetworks.com]
Sent: Monday, August 28, 2017 4:10 PM
To: Van Haaren, Harry <redacted>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] eal: added new `rte_lcore_is_service_lcore` API.

On Mon, Aug 28, 2017 at 01:49:37PM +0000, Van Haaren, Harry wrote:

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From: Pavan Nikhilesh Bhagavatula [mailto:pbhagavatula@caviumnetworks.com]
Sent: Monday, August 28, 2017 12:33 PM
To: Van Haaren, Harry <redacted>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] eal: added new `rte_lcore_is_service_lcore` API.

On Mon, Aug 28, 2017 at 10:59:51AM +0000, Van Haaren, Harry wrote:

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From: Pavan Nikhilesh [mailto:pbhagavatula@caviumnetworks.com]
Sent: Wednesday, August 23, 2017 4:10 PM
To: dev@dpdk.org
Cc: Van Haaren, Harry <redacted>; Pavan Nikhilesh
[off-list ref]
Subject: [dpdk-dev] [PATCH] eal: added new `rte_lcore_is_service_lcore` API.

This API can be used to test if an lcore(EAL thread) is a service lcore.

Signed-off-by: Pavan Nikhilesh <redacted>
---
 lib/librte_eal/common/include/rte_lcore.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/lib/librte_eal/common/include/rte_lcore.h

b/lib/librte_eal/common/include/rte_lcore.h
index 50e0d0f..7854ea1 100644

--- a/lib/librte_eal/common/include/rte_lcore.h
+++ b/lib/librte_eal/common/include/rte_lcore.h

@@ -180,6 +180,24 @@ rte_lcore_is_enabled(unsigned lcore_id)
 }

 /**
+ * Test if an lcore is service lcore.
+ *
+ * @param lcore_id
+ *   The identifier of the lcore, which MUST be between 0 and
+ *   RTE_MAX_LCORE-1.
+ * @return
+ *   True if the given lcore is service; false otherwise.
+ */
+static inline int
+rte_lcore_is_service_lcore(unsigned lcore_id)
+{
+	struct rte_config *cfg = rte_eal_get_configuration();
+	if (lcore_id >= RTE_MAX_LCORE)
+		return 0;
+	return cfg->lcore_role[lcore_id] == ROLE_SERVICE;
+}

No header file and Static inline - so this is only to be used internally in the service

cores library?

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If so, the function should actually be used, instead of only added but not used in the

library itself.

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The enum rte_lcore_role_t has ROLE_SERVICE which tells that a particular lcore is
a service lcore as well as an EAL thread some libraries such as rte_timer allow
specific operations only over EAL threads.

Understood that role of cores is important, and that rte_timer might require this

information.

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The rte_timer lib uses the rte_is_lcore_enabled() call to check if a lcore is an
EAL thread, Which checks if the lcore role is  ROLE_RTE. But it should also
allow timers to be registered on a service core as processing those timers can
be done on them.

No problem from me here either - although it's the Timers library maintainer that should

check this.

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This new function allows such libraries to check if the role is
ROLE_SERVICE and allow those operations.

If the timers library requires information about service-cores, it should use a public API

to retrieve that information. Having "internal" functions between libraries is not nice.

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I think a better design would be to add this function as a public function, (add it to the

.map files etc) and then call the public function from the timers library.

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Does that sound like a good solution? -Harry

The file rte_lcore.h is in librte_eal/common/include I couldn't find a .map
file for eal/common and also other functions that are present in rte_lcore.h
aren't mapped in eal/linuxapp or eal/bsdapp.
I think it is fine as the functions are static inline.

-Pavan

OK - I was looking at this from a service core library POV. The intent seems to be to update EAL in order to allow detection of a core having a ROLE_SERVICE. Now I see your intent better, no problem with the approach. Correct that static-inline functions don't need .map file entries (cause they're inlined :)

One technical issue:

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+	if (lcore_id >= RTE_MAX_LCORE)
+		return 0;

This should return a -ERROR value, as 0 is a valid return value that should indicate one thing (and one thing only) "not a service core".

The function function follows the same structure as rte_lcore_is_enabled i.e.
returns either true(1) or false(0). So, I think returning 0 would be fine?. If
not I'll gladly send a v2.

Thanks for the inputs :). -Pavan.

Please spin a v2 and I'll Ack.

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Currently, the only rte_timer library has this specific role check. The
following patch shows the usage in rte_timer library.

http://dpdk.org/dev/patchwork/patch/27819/

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Or am I mis-understanding the intent?

-Harry

Thanks,
Pavan.