Re: [PATCH 00/31] Skip automatic zero-init of large arrays / structs in I/O paths

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jun 10, 2025 at 02:49:02PM +0200, Philippe Mathieu-Daudé wrote:
> On 10/6/25 14:36, Daniel P. Berrangé wrote:
> > This series is an extension of Stefan's proposal:
> > 
> >    https://lists.nongnu.org/archive/html/qemu-devel/2025-06/msg00736.html
> > 
> > It used '-Wframe-larger-than=4096' to identify all code locations
> > with more than 4k on the stack. Any locations in the I/O paths
> > were chosen to avoid automatic zero-init, to eliminate the performance
> > overhead of the automatic initialization.
> 
> Should we eventually add it to our default CFLAGS?

You mean as a way to impose a hard limit on stack frame size ?

FWIW, the VNC server is biggest at 100kb, but we have a large
number of other big frames - here's a sorted list of frame
sizes vs frequency

      1 103696 
      2 69664 
     46 49184 
      4 42608 
     23 32880 
     23 32864 
      1 32832 
      1 28688 
     36 24800 
     10 24784 
      1 22240 
     21 21760 
      1 20624 
      1 17536 
      2 17168 
      1 16592 
      1 16576 
      1 16544 
      1 16512 
      2 16480 
      2 16464 
      1 16448 
      4 16432 
      1 15136 
      1 12960 
      1 12336 
      1 12048 
      1 10064 
      5 9184 
      1 8832 
      1 8784 
      1 8576 
      1 8448 
      2 8400 
      1 8384 
      2 8304 
      1 8272 
      4 8256 
      1 8240 
      4 8224 
      7 8208 
      2 7120 
      1 6800 
      1 5856 
      1 4928 
      2 4560 
      1 4464 
      1 4336 
      2 4256 
      1 4240 
      2 4224 
      4 4208 
      9 4176 
      9 4160 
     40 4144 
     68 4128 
      9 4112 



With regards,
Daniel
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