Why using Stopwatch in Blazor Server App cause slower code execution - performance

Question

I have a Blazor Server App .Net7 with a single page with this code:
#page "/"
#using System.Diagnostics
<PageTitle>Counter</PageTitle>
<button #onclick=OnCalcClick>Count</button>
<div>Elapsed Time: #time ms</div>
<div>Elapsed Time Stopwatch: #timeHigh ms</div>
#code{
long result = 0;
double time = 0;
long timeHigh = 0;
void OnCalcClick() {
//Stopwatch s = new Stopwatch();
//s.Start();
var start = DateTime.UtcNow;
for (long i = 0; i < 1000000000; i++)
result ++;
//s.Stop();
var stop = DateTime.UtcNow;
//timeHigh = s.ElapsedMilliseconds;
time = (stop - start).TotalMicroseconds;
}
}
If I run the App in Release mode without debugging, I get the execution time about 250 ms.
If I comment using of DateTime and uncomment the Stopwatch, I get the execution time about 750 ms
If I uncomment everething, I get the same time with both measurement method and this time is about 750 ms.
I tried to do this multiple times, but results are the same.
So, it seems, Stopwatch makes the execution slower, but why?

Answer 1

Here's my test version of your code. I:
Dropped the loop by an order of 10.
Separated out each test
I can't see any major difference in execution times. Debug is slower, but that's expected. What am I missing from your testing?
#page "/"
#using System.Diagnostics
<PageTitle>Counter</PageTitle>
<div class="alert alert-info">
<div class="mb-2" >Elapsed Time: #time1 ms</div>
<button class="btn btn-sm btn-primary" #onclick=OnCalcClick>Count</button>
</div>
<div class="alert alert-info">
<div class="mb-2">Elapsed Time Stopwatch: #timeHigh2 ms</div>
<button class="btn btn-sm btn-primary" #onclick=OnCalcClickWithTimer>Count Timed</button>
</div>
<div class="alert alert-info">
<div>Elapsed Time: #time3 ms</div>
<div class="mb-2">Elapsed Time Stopwatch: #timeHigh3 ms</div>
<button class="btn btn-sm btn-primary" #onclick=OnCalcClickWithAll>Count Timed</button>
</div>
#code {
long result1 = 0;
double time1 = 0;
long result2 = 0;
double time2 = 0;
long timeHigh2 = 0;
long result3 = 0;
double time3 = 0;
long timeHigh3 = 0;
void OnCalcClick()
{
var start = DateTime.UtcNow;
for (long i = 0; i < 100000000; i++)
result1++;
var stop = DateTime.UtcNow;
time1 = (stop - start).TotalMilliseconds;
}
void OnCalcClickWithTimer()
{
Stopwatch s = new Stopwatch();
s.Start();
for (long i = 0; i < 100000000; i++)
result2++;
s.Stop();
timeHigh2 = s.ElapsedMilliseconds;
}
void OnCalcClickWithAll()
{
Stopwatch s = new Stopwatch();
s.Start();
var start = DateTime.UtcNow;
for (long i = 0; i < 100000000; i++)
result3++;
s.Stop();
var stop = DateTime.UtcNow;
timeHigh3 = s.ElapsedMilliseconds;
time3 = (stop - start).TotalMilliseconds;
}
}
Result in release mode:
And debug: