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Re: 5.0.0-rc3 : Opcode 1f 12 0f 00 (7ce003e4) leaked temporaries

From: Peter Maydell
Subject: Re: 5.0.0-rc3 : Opcode 1f 12 0f 00 (7ce003e4) leaked temporaries
Date: Fri, 17 Apr 2020 12:14:29 +0100

On Fri, 17 Apr 2020 at 12:00, BALATON Zoltan <address@hidden> wrote:
> On Fri, 17 Apr 2020, Peter Maydell wrote:
> > And yes, debug
> > is slower (it builds QEMU without optimization enabled
> > so it's easier to debug QEMU in gdb, and it turns on
> > various extra sanity checks.)
> Last time I've looked I've found it effectively disables TB cache (at
> least with PPC) because one of those checks forces a flush which is the
> main source of the slowness with --enable-debug. Not sure if this could be
> avoided, I didn't know about --disable-tcg-debug Philippe suggested so
> haven't tested that.

It's not supposed to disable TB caching, and in my experience
it does not (no TB caching at all is incredibly slow). If it's
doing that on PPC that would be worth investigating.

I do almost all of my work and local testing with --enable-debug,
so I notice if it's slowed down to the extent that "no TB caching"
would involve. It is naturally slower than the non-debug config
both because of some extra checking and also because all the C
code is being compiled at -O0 rather than -O2.

-- PMM

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