Charles-Francois Natali <[email protected]> added the comment:
A couple remarks on BFS-based patch:
- nothing guarantees that you'll get a msec resolution
- gettimeofday returns you wall clock time: if a process that modifies time is
running, e.g. ntpd, you'll likely to run into trouble. the value returned is
_not_ monotonic, but clock_gettime(CLOCK_MONOTONIC) is
- inline functions are used, but it's not ANSI
- static inline long double get_timestamp(void) {
struct timeval tv;
GETTIMEOFDAY(&tv);
return (long double) tv.tv_sec + tv.tv_usec * 0.000001;
}
the product is computed as double, and then promoted as (long double).
- the code uses a lot of floating point calculation, which is slower than
integer
Otherwise:
"- You know, I almost wonder whether this whole issue could be fixed by just
adding a user-callable function to optionally set a thread priority number.
For example:
sys.setpriority(n)
Modify the new GIL code so that it checks the priority of the currently running
thread against the priority of the thread that wants the GIL. If the running
thread has lower priority, it immediately drops the GIL."
The problem with this type of fixed-priority is starvation. And it shouldn't be
up to the user to set the priorities. And some threads can mix I/O and CPU
intensive tasks.
> It's a dual-core Linux x86-64 system. But, looking at the patch again, the
> reason is obvious:
>
> #define CHECK_SLICE_DEPLETION(tstate) (bfs_check_depleted || (tstate
> >tick_counter % 1000 == 0))
>
> `tstate->tick_counter % 1000` is replicating the behaviour of the old GIL,
> which based its speculative operation on the number of elapsed opcodes (and
> which also gave bad latency numbers on the regex workload).
I find this suspicous too. I haven't looked at the patch in detail, but what
does the number of elapsed opcodes offers you over the timesplice expiration
approach ?
----------
nosy: +neologix
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