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Re: [PATCH] x86/time: adjust handling of negative delta in stime2tsc()
- To: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 26 Mar 2026 09:05:21 +0100
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Delivery-date: Thu, 26 Mar 2026 08:05:26 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 25.03.2026 18:57, Roger Pau Monné wrote:
> On Tue, Feb 10, 2026 at 11:04:59AM +0100, Jan Beulich wrote:
>> --- a/xen/arch/x86/time.c
>> +++ b/xen/arch/x86/time.c
>> @@ -1176,20 +1176,26 @@ uint64_t __init calibrate_apic_timer(voi
>> return elapsed * CALIBRATE_FRAC;
>> }
>>
>> -u64 stime2tsc(s_time_t stime)
>> +uint64_t stime2tsc(s_time_t stime)
>> {
>> - struct cpu_time *t;
>> - struct time_scale sys_to_tsc;
>> - s_time_t stime_delta;
>> + const struct cpu_time *t = &this_cpu(cpu_time);
>> + s_time_t stime_delta = stime - t->stamp.local_stime;
>> + int64_t delta = 0;
>
> Why do you make delta a signed integer, the value returned by
> scale_delta() is unsigned.
I guess purely mechanically, as deltas usually want to be signed. Changed.
>> - t = &this_cpu(cpu_time);
>> - sys_to_tsc = scale_reciprocal(t->tsc_scale);
>> + /*
>> + * While for reprogram_timer() the capping at 0 isn't relevant (the
>> returned
>
> The capping might want mentioning in the function prototype, as maybe
> new users expect stime2tsc() to return TSC values from times in the
> past.
Can do, sure.
Jan
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