From: "Wiles, Keith" <keith.wiles@intel.com>
To: Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>
Cc: "stephen@networkplumber.org" <stephen@networkplumber.org>,
"thomas@monjalon.net" <thomas@monjalon.net>,
"dev@dpdk.org" <dev@dpdk.org>,
Jerin Jacob Kollanukkaran <jerinj@marvell.com>
Subject: Re: [dpdk-dev] [EXT] Re: [PATCH v2 2/2] eal: roundup tsc frequency when estimating it
Date: Sat, 16 Mar 2019 18:22:44 +0000 [thread overview]
Message-ID: <B330BE86-D922-4951-959F-CC841E955DFD@intel.com> (raw)
Message-ID: <20190316182244.A17Uqx5ZOLv8MBA7IaQGgGwKz0jC6xPebRwuDST_R2A@z> (raw)
In-Reply-To: <a30e5b07274ab5c42a8e5206544f961e6fffecdd.camel@marvell.com>
> On Mar 16, 2019, at 12:56 PM, Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com> wrote:
>
> On Sat, 2019-03-16 at 17:18 +0000, Wiles, Keith wrote:
>>> On Mar 16, 2019, at 10:06 AM, Pavan Nikhilesh Bhagavatula <
>>> pbhagavatula@marvell.com> wrote:
>>>
>>> On Sat, 2019-03-16 at 14:42 +0000, Wiles, Keith wrote:
>>>>> On Mar 16, 2019, at 2:03 AM, Pavan Nikhilesh Bhagavatula <
>>>>> pbhagavatula@marvell.com> wrote:
>>>>>
>>>>> From: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>>>
>>>>> When estimating tsc frequency using sleep/gettime round it up
>>>>> to
>>>>> the
>>>>> nearest multiple of 10Mhz for more accuracy.
>>
>> How does rounding up the TSC value become more accurate, If the value
>> is 1 cycles more then it should be then your macro would round down
>> and if it is 1 cycle greater than 1E7 it would round up.
>
> Example in case of RTE_ARM_EAL_RDTSC_USE_PMU enabled
>
> Before roundup : 1400000979
> After roundup : 1400000000
> EAL: TSC frequency is ~1400000000 Hz
>
>
> Before roundup : 1399999060
> After roundup : 1400000000
> EAL: TSC frequency is ~1400000000 Hz
>
>>>>> Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
>>>>> ---
>>>>> Useful in case of ARM64 if we enable RTE_ARM_EAL_RDTSC_USE_PMU,
>>>>> get_tsc_freq_arch() will return 0 as there is no instruction to
>>>>> determine
>>>>> the clk of PMU and eal falls back to sleep(1).
>>>>>
>>>>> lib/librte_eal/common/eal_common_timer.c | 4 ++--
>>>>> lib/librte_eal/linuxapp/eal/eal_timer.c | 2 +-
>>>>> 2 files changed, 3 insertions(+), 3 deletions(-)
>>
>> It appears you did not use the head of the master as linuxapp is now
>> just linux and freebsdapp is freebsd. You need to rebase to the head
>> of master and send a new version.
>>>>> diff --git a/lib/librte_eal/common/eal_common_timer.c
>>>>> b/lib/librte_eal/common/eal_common_timer.c
>>>>> index dcf26bfea..1358bbed0 100644
>>>>> --- a/lib/librte_eal/common/eal_common_timer.c
>>>>> +++ b/lib/librte_eal/common/eal_common_timer.c
>>>>> @@ -69,7 +69,7 @@ estimate_tsc_freq(void)
>>>>> /* assume that the sleep(1) will sleep for 1 second */
>>>>> uint64_t start = rte_rdtsc();
>>>>> sleep(1);
>>>>> - return rte_rdtsc() - start;
>>>>> + return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, 1E7);
>>
>> The 1E7 is a magic number convert this to a meaningful define.
>
> 1E7 ~ 10Mhz will convert to a macro.
>
>>>>> }
>>>>>
>>>>> void
>>>>> @@ -83,7 +83,7 @@ set_tsc_freq(void)
>>>>> if (!freq)
>>>>> freq = estimate_tsc_freq();
>>>>>
>>>>> - RTE_LOG(DEBUG, EAL, "TSC frequency is ~%" PRIu64 "
>>>>> KHz\n", freq
>>>>> / 1000);
>>>>> + RTE_LOG(INFO, EAL, "TSC frequency is ~%" PRIu64 "
>>>>> Hz\n", freq);
>>>>> eal_tsc_resolution_hz = freq;
>>>
>>> I missed this log will remove it in the next version.
>>>
>>>>> }
>>>>>
>>>>> diff --git a/lib/librte_eal/linuxapp/eal/eal_timer.c
>>>>> b/lib/librte_eal/linuxapp/eal/eal_timer.c
>>>>> index bc8f05199..864d6ef29 100644
>>>>> --- a/lib/librte_eal/linuxapp/eal/eal_timer.c
>>>>> +++ b/lib/librte_eal/linuxapp/eal/eal_timer.c
>>>>> @@ -248,7 +248,7 @@ get_tsc_freq(void)
>>>>>
>>>>> double secs = (double)ns/NS_PER_SEC;
>>>>> tsc_hz = (uint64_t)((end - start)/secs);
>>>>> - return tsc_hz;
>>>>> + return RTE_ALIGN_MUL_NEAR(tsc_hz, 1E7);
>>>>
>>>> Maybe I missed an email about this, but why would I want the TSC
>>>> hz
>>>> rounded here? I do not mind the macro just the fact that we are
>>>> changing TSC hz value. If the TSC value is wrong then we need to
>>>> fix
>>>> the value, but I do not see it being wrong here.
>>>
>>> Since in this function nanosleep might not be cycle accurate we
>>> need to
>>> round it up.
>>>
>>> Please note that estimation only applies when get_tsc_freq_arch()
>>> fails. i.e there is no CPU instruction that specifies the cyc/sec.
>>>
>>> As I mentioned in the patch notes
>>> "Useful in case of ARM64 if we enable RTE_ARM_EAL_RDTSC_USE_PMU,
>>> get_tsc_freq_arch() will return 0 as there is no instruction to
>>> determine the clock of PMU and eal falls back to
>>> sleep(1)/nanosleep.”
>>
>> OK, I looked at the changes and the code for setting the TSC again. I
>> would have not handled the setting of TSC in the way it was done, but
>> that is not your problem. I agree the changes do look ok, the only
>> problem I have is the new macro will roundup or down depending on the
>> value. In your statement you are wanting to roundup the values.
>>
>> If the sleep/nanosleep is less than a second for some reason, then
>> your macro would round it down is that what we wanted? I guess my
>> point is you are assuming the TSC calculation will always be less
>> than a second (with sleep) and the macro would round up depending on
>> the value calculated using the sleep/nanosleep.
>>
>> I was playing with these MUL macros and I am not sure they do what we
>> expect in the case of the multiple value is much closer to the value
>> passed.
>>
>> If we have a v = 10001 and multiple to 1000 we have the following:
>>
>> RTE_ALIGN_MUL_CEIL(10001, 1000)
>> (10001 + (1000 - 1)) / (1000 * 1000)
> ((10001 + (1000 - 1)) / 1000) * 1000
>> (10001 + 999) / 1000000
>> 20000 / 1000000
>> Result: 0
>
> ((10001 + (1000 - 1) / 1000) * 1000
> ((10001 + 999) / 1000) * 1000
> (11000/1000) * 1000
> 11 * 1000
>
> Result : 11000
>
>>
>> RTE_ALIGN_MUL_FLOOR(10001, 1000)
>> (10001 / (1000 * 1000))
> (10001 / 1000) * 1000
>> (10001 / 1000000)
>> Result: 0
> 10.001 * 1000
>
> Result : 1000
Ooops, too many parans and missed it.
Then we can get a new version and that should be OK.
I will add my $0.02 then:
Reviewed-by: Keith Wiles<keith.wiles>
>
>>
>> Unless I am wrong here the value v must be over a 1,000,000 to make
>> these macros work or the value v to be greater than (mul * mul) in
>> all cases or zero is the result. It may work for the TSC values as we
>> are using a small mul value compared to the TSC value. If DPDK was
>> ported to a slower machine it could be also zero.
>
> Unless we have machines that run at freq < 10Mhz this scheme will
> always work.
> If we have such machines lets hope that they have a CPU instruction
> that tells us the cyc/sec.
>
>>
>> I think we need to fix the macros and rethink how TSC is set here.
>>
>>>>> }
>>>>> #endif
>>>>> return 0;
>>>>> --
>>>>> 2.21.0
>>>>>
>>>>
>>>> Regards,
>>>> Keith
>>
>> Regards,
>> Keith
>>
>
> Regards,
> Pavan.
Regards,
Keith
next prev parent reply other threads:[~2019-03-16 18:22 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-29 8:32 [dpdk-dev] [PATCH] " Pavan Nikhilesh
2018-11-29 9:08 ` Jerin Jacob
2018-11-29 21:21 ` Stephen Hemminger
2018-11-30 7:17 ` Pavan Nikhilesh
2019-03-16 7:03 ` [dpdk-dev] [PATCH v2 1/2] eal: add macro to align value to the nearest multiple Pavan Nikhilesh Bhagavatula
2019-03-16 7:03 ` Pavan Nikhilesh Bhagavatula
2019-03-16 7:03 ` [dpdk-dev] [PATCH v2 2/2] eal: roundup tsc frequency when estimating it Pavan Nikhilesh Bhagavatula
2019-03-16 7:03 ` Pavan Nikhilesh Bhagavatula
2019-03-16 14:42 ` Wiles, Keith
2019-03-16 14:42 ` Wiles, Keith
2019-03-16 15:06 ` [dpdk-dev] [EXT] " Pavan Nikhilesh Bhagavatula
2019-03-16 15:06 ` Pavan Nikhilesh Bhagavatula
2019-03-16 17:18 ` Wiles, Keith
2019-03-16 17:18 ` Wiles, Keith
2019-03-16 17:56 ` Pavan Nikhilesh Bhagavatula
2019-03-16 17:56 ` Pavan Nikhilesh Bhagavatula
2019-03-16 18:22 ` Wiles, Keith [this message]
2019-03-16 18:22 ` Wiles, Keith
2019-03-16 18:27 ` Pavan Nikhilesh Bhagavatula
2019-03-16 18:27 ` Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` [dpdk-dev] [PATCH v3 1/2] eal: add macro to align value to the nearest multiple Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` [dpdk-dev] [PATCH v3 2/2] eal: roundup tsc frequency when estimating Pavan Nikhilesh Bhagavatula
2019-03-16 19:01 ` Pavan Nikhilesh Bhagavatula
2019-03-27 22:43 ` Thomas Monjalon
2019-03-27 22:43 ` Thomas Monjalon
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