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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 1 Apr 2020 17:26:29 -0700
Message-ID: <CAKwvOdnO2=yjEerw50b_C2vrgdCh2es6ZRfQpBRVR9RCrvwi6Q@mail.gmail.com>
Subject: Re: [PATCH v3] bitfield.h: add FIELD_MAX() and field_max()
To:     Alex Elder <elder@linaro.org>,
        Maxim Kuvyrkov <maxim.kuvyrkov@linaro.org>
Cc:     Arnd Bergmann <arnd@arndb.de>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        "David S. Miller" <davem@davemloft.net>,
        Johannes Berg <johannes@sipsolutions.net>,
        Jakub Kicinski <kuba@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Masahiro Yamada <masahiroy@kernel.org>,
        Nathan Chancellor <natechancellor@gmail.com>,
        Network Development <netdev@vger.kernel.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>
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On Wed, Apr 1, 2020 at 4:18 PM Alex Elder <elder@linaro.org> wrote:
>
> On 4/1/20 5:26 PM, Nick Desaulniers wrote:
> >
> > mainline is hosed for aarch64 due to some dtc failures.  I'm not sure
> > how TCWG's CI chooses the bisection starting point, but if mainline
> > was broken, and it jumped back say 300 commits, then the automated
> > bisection may have converged on your first patch, but not the second.
>
> This is similar to the situation I discussed with Maxim this
> morning.  A different failure (yes, DTC related) led to an
> automated bisect process, which landed on my commit. And my
> commit unfortunately has the the known issue that was later
> corrected.
>
> Maxim said this was what started the automated bisect:
> ===
> +# 00:01:41 make[2]: *** [arch/arm64/boot/dts/ti/k3-am654-base-board.dtb] Error 2
> +# 00:01:41 make[2]: *** [arch/arm64/boot/dts/ti/k3-j721e-common-proc-board.dtb] Error 2
> +# 00:01:41 make[1]: *** [arch/arm64/boot/dts/ti] Error 2
> +# 00:01:41 make: *** [dtbs] Error 2

DTC thread:
https://lore.kernel.org/linux-arm-kernel/20200401223500.224253-1-ndesaulniers@google.com/

Maxim, can you describe how the last known good sha is chosen?  If you
persist anything between builds, like ccache dir, maybe you could
propagate a sha of the last successful build, updating it if no
regression occurred?  Then that can always be a precise last known
good sha.  Though I don't know if the merge commits complicate this.
-- 
Thanks,
~Nick Desaulniers