netdev - Re: [PATCH] openvswitch: use ktime_get_ts64() instead of ktime_get

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Message-ID: <CAK8P3a1pTbrk5u-CcCXReTYk-d7X30AVmpmtrvoWLOiaFGTzhQ@mail.gmail.com>
Date:   Tue, 28 Nov 2017 09:50:06 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Pravin Shelar <pshelar@....org>
Cc:     Pravin Shelar <pshelar@...ira.com>,
        "David S. Miller" <davem@...emloft.net>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Tonghao Zhang <xiangxia.m.yue@...il.com>,
        Jiri Benc <jbenc@...hat.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jarno Rajahalme <jarno@....org>,
        Yi-Hung Wei <yihung.wei@...il.com>,
        Yi Yang <yi.y.yang@...el.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        ovs dev <dev@...nvswitch.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] openvswitch: use ktime_get_ts64() instead of ktime_get_ts()

On Tue, Nov 28, 2017 at 5:59 AM, Pravin Shelar <pshelar@....org> wrote:
> On Mon, Nov 27, 2017 at 5:11 PM, Arnd Bergmann <arnd@...db.de> wrote:
>> timespec is deprecated because of the y2038 overflow, so let's convert
>> this one to ktime_get_ts64(). The code is already safe even on 32-bit
>> architectures, since it uses monotonic times. On 64-bit architectures,
>> nothing changes, while on 32-bit architectures this avoids one
>> type conversion.
>>
>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> ---
>>  net/openvswitch/flow.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/net/openvswitch/flow.c b/net/openvswitch/flow.c
>> index dbe2379329c5..76d050aba7a4 100644
>> --- a/net/openvswitch/flow.c
>> +++ b/net/openvswitch/flow.c
>> @@ -56,12 +56,12 @@
>>
>>  u64 ovs_flow_used_time(unsigned long flow_jiffies)
>>  {
>> -       struct timespec cur_ts;
>> +       struct timespec64 cur_ts;
>>         u64 cur_ms, idle_ms;
>>
>> -       ktime_get_ts(&cur_ts);
>> +       ktime_get_ts64(&cur_ts);
>>         idle_ms = jiffies_to_msecs(jiffies - flow_jiffies);
>> -       cur_ms = (u64)cur_ts.tv_sec * MSEC_PER_SEC +
>> +       cur_ms = (u64)(u32)cur_ts.tv_sec * MSEC_PER_SEC +
>
> I am not sure why is tv_sec converted to u32.

It was a micro-optimization that I did to turn a 's64 * constant -> s64'
operation into a cheaper 's32 * constant -> s64' operation. If you
prefer, I can sent it again with a comment, or drop the two
casts.

        Arnd