For the case where many tasks being popped from the central queue cannot
be dispatched to the local DSQ of the target CPU, we will keep bouncing
them to the fallback DSQ and continue the dispatch_to_cpu loop until we
find one which can be dispatch to the local DSQ of the target CPU.
In a contrived case, it might be so that all tasks pin themselves to
CPUs != target CPU, and due to their affinity cannot be dispatched to
that CPU's local DSQ. If all of them are filling up the central queue,
then we will keep looping in the dispatch_to_cpu loop and eventually run
out of slots for the dispatch buffer. The nr_mismatched counter will
quickly rise and sched-ext will notice the error and unload the BPF
scheduler.
To remedy this, ensure that we break the dispatch_to_cpu loop when we
can no longer perform a dispatch operation. The outer loop in
central_dispatch for the central CPU should ensure the loop breaks when
we run out of these slots and schedule a self-IPI to the central core,
and allow sched-ext to consume the dispatch buffer before restarting the
dispatch loop again.
A basic way to reproduce this scenario is to do:
taskset -c 0 perf bench sched messaging
The error in the kernel will be:
sched_ext: BPF scheduler "central" errored, disabling
sched_ext: runtime error (dispatch buffer overflow)
bpf_prog_6a473147db3cec67_dispatch_to_cpu+0xc2/0x19a
bpf_prog_c9e51ba75372a829_central_dispatch+0x103/0x1a5
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
We should explicitly use u64 for hweight_gen to prevent the following
build failures on 32-bit architectures:
scheds/kernel-examples/scx_flatcg.p/scx_flatcg.bpf.skel.h: In function ‘scx_flatcg__assert’:
scheds/kernel-examples/scx_flatcg.p/scx_flatcg.bpf.skel.h:3523:9: error: static assertion failed: "unexpected size of \'hweight_gen\'"
3523 | _Static_assert(sizeof(s->data->hweight_gen) == 8, "unexpected size of 'hweight_gen'");
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
When printing scheduler statistics we use %lu to print u64 values, that
works well on 64-bit architectures, but on 32-bit architectures we get
errors like the following:
106 | printf("total :%10lu local:%10lu queued:%10lu lost:%10lu\n",
| ~~~~^
| |
| long unsigned int
| %10llu
107 | skel->bss->nr_total,
| ~~~~~~~~~~~~~~~~~~~
| |
| u64 {aka long long unsigned int}
Fix this by using the proper format %llu.
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
Use compiler's built-in stack initialization instead of memset().
In this way we can get rid of the string.h include and make
cross-compilation easier in certain small environments (i.e., arm).
Signed-off-by: Andrea Righi <andrea.righi@canonical.com>
There's a fairly comprehensive README in the kernel's tools/sched_ext
directory which describes each of the example schedulers. Let's pull it
into this repository, and split it into the various subdirectories
containing the kernele-examples/ schedulers, and the rust-user/
schedulers.
Signed-off-by: David Vernet <void@manifault.com>
SCX_DSQ_GLOBAL now does not support vtime dispatching. scx_simple uses
it to do vtime scheduling, so let's update it to create and use a
separate DSQ that it can both FIFO and PRIQ dispatch to.
Signed-off-by: David Vernet <void@manifault.com>
