On Mon, Dec 02, 2024 at 01:53:02PM +0000, Stuart Henderson wrote:
> Thought I'd take a look at a kernel profile from a machine which is
> fairly "interesting" in terms of kernel spin. (Running -current).
> 
> In the attached output from running "btrace kprofile.bt" I have a
> lot of time accounted for under syscall+0x5c4, which has _kernel_lock
> directly next to it in the traces, and I was wondering what that is.
> Bit confused by disasm of trap.o but my guess is that it might be
> a lock relating to dt(4) itself, is that right?
 
I think this is the bit of syscall that grabs the kernel lock for any
syscall not marked NOLOCK. In your case this is mostly fstat*, open*
or the bits under syscall+0x5e7.

Your system does a lot of parallel disk IO and that is all still using the
KERNEL_LOCK.

-- 
:wq Claudio