From: Thomas Monjalon [mailto:thomas@monjalon.net]
Sent: Wednesday, May 5, 2021 8:51 AM

05/05/2021 08:26, Morten Brørup:

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From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas

Monjalon

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Sent: Wednesday, May 5, 2021 8:14 AM

04/05/2021 21:12, Morten Brørup:

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From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Thomas

Monjalon

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Sent: Tuesday, May 4, 2021 6:50 PM

29/04/2021 04:10, Min Hu (Connor):

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Currently, the mp uses gettimeofday() API to get the time,

and

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used

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as

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timeout parameter.

But the time which gets from gettimeofday() API isn't

monotonically

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increasing. The process may fail if the system time is

changed.

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This fixes it by using clock_gettime() API with monotonic

attribution.

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Fixes: 783b6e54971d ("eal: add synchronous multi-process

communication")

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Fixes: f05e26051c15 ("eal: add IPC asynchronous request")
Cc: stable@dpdk.org

Signed-off-by: Chengwen Feng <redacted>
Signed-off-by: Min Hu (Connor) <redacted>
---

[...]

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--- a/lib/eal/common/eal_common_proc.c	
+++ b/lib/eal/common/eal_common_proc.c
-	if (gettimeofday(&now, NULL) < 0) {
-		RTE_LOG(ERR, EAL, "Cannot get current time\n");
-		goto no_trigger;
-	}
-	ts_now.tv_nsec = now.tv_usec * 1000;
-	ts_now.tv_sec = now.tv_sec;
+	clock_gettime(CLOCK_MONOTONIC, &ts_now);

Why not testing the return value?

Because it is guaranteed not to fail. Ref:
https://linux.die.net/man/3/clock_gettime
https://www.freebsd.org/cgi/man.cgi?query=clock_gettime

I see "return 0 for success, or -1 for failure".
Where is it said it cannot fail?

I'm sorry about being unclear. Referring to the "Errors" chapter in

the function's man page, this function call is guaranteed not to fail
with these parameters. So there is no need to check the return value.

I don't agree.
Especially for this error:
"The clk_id specified is not supported on this system."
How can you be sure it is always supported for any system
we try to run this code now and in future experiments?

I referred to both Linux and BSD man pages because they say that it is defined there. This should cover current supported systems, excl. Windows, which doesn't have gettimeofday() or clock_gettime() anyway.

However, for future operating systems that might be supported by DPDK, you are correct that CLOCK_MONOTONIC is optional.
Ref: https://pubs.opengroup.org/onlinepubs/009695399/basedefs/time.h.html

This can be fixed by adding:
#if !defined(CLOCK_MONOTONIC)
#error CLOCK_MONOTONIC is not defined.
#endif

If we only check the return value at runtime, the function would fail every time on a system without CLOCK_MONOTONIC, and eal_common_proc.c would need to be fixed anyway. It's better to catch at compile time.