Re: [PATCH sched_ext/for-7.3-fixes] sched_ext: Generate qseq from a per-task counter

[Tejun Heo]

Hello, Kuba.

On Fri, Oct 02, 2026 at 08:52:41PM +0000, Kuba Piecuch wrote:
> +	do {
> +		p->scx.ops_qseq++;
> +		qseq = (unsigned long)p->scx.ops_qseq << SCX_OPSS_QSEQ_SHIFT;
> +	} while (unlikely(!qseq));

Maybe wrap the counter where the QSEQ field wraps instead of looping?

	p->scx.ops_qseq = ((p->scx.ops_qseq + 1) &
			   (SCX_OPSS_QSEQ_MASK >> SCX_OPSS_QSEQ_SHIFT)) ?: 1;
	qseq = (unsigned long)p->scx.ops_qseq << SCX_OPSS_QSEQ_SHIFT;

On 32bit, the shift drops the top two bits of the counter, so the mask is
what keeps the counter from reaching a value that shifts to 0.

Thanks.

-- 
tejun