Re: [PATCH 00/11] Enable non-stop mode by default for remote targets

[Pedro Alves <pedro@palves.net>]

On 2026-05-18 19:32, Mohamed Bouhaouel wrote:
> From: "Bouhaouel, Mohamed" <mohamed.bouhaouel@intel.com>
> 
> This series makes remote targets operate in non-stop mode if the target
> announces QNonStop support and 'maint set target-non-stop’ is set to
> ‘auto', aligning the behavior with the Linux native target.

This wasn't done before for a reason.  It's that 'maint set target-non-stop on’
does not support all the features the all-stop variant of the remote protocol.

Specifically, off the top of my head:

  - there is no alternative to the O packet.  Those can be sent while the
    target is running as if they were a stop reply, but that doesn't work
    in non-stop mode.

    See remote_target::wait_as:

       case 'O':		/* Console output.  */

  - remote file I/O support does not work.  Similar to the O packet.

    See remote_target::wait_as:

       case 'F':		/* File-I/O request.  */

  - packet efficiency.  With non-stop, GDB suspends and resumes each
    thread individually.

     - on the resumption side, that is mitigated by GDB coalescing
       vCont packets.  when you e.g. "continue", gdb core does one
       target_resume call per thread, but the remote target backend
       does not resume the thread immediately.  Instead, it defers
       the resume until infrun calls target_commit_resumed().

     - on the stopping side, however, there is no support for aggregation.
       The server reports each thread stop with its own separate stop reply
       notification.


So it's plausible that there may some stubs out there that do support
non-stop mode, but they also support e.g., file I/O.  Enabling non-stop by
default for those might not be the correct choice.

Or maybe the performance degrades visibly.  Maybe there are some
mitigating factors, like, maybe it won't matter that much if we have
displaced stepping.

My point is, this needs to be a considered change, not just "to align with linux".

Pedro Alves