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Rao" Subject: Re: [PATCH v4 2/6] powerpc/idle: Add accessor function to always read latest idle PURR To: "Gautham R. Shenoy" , Kamalesh Babulal , Michael Ellerman , Nathan Lynch , Vaidyanathan Srinivasan , Tyrel Datwyler References: <1585308760-28792-1-git-send-email-ego@linux.vnet.ibm.com> <1585308760-28792-3-git-send-email-ego@linux.vnet.ibm.com> In-Reply-To: <1585308760-28792-3-git-send-email-ego@linux.vnet.ibm.com> MIME-Version: 1.0 User-Agent: astroid/v0.15-13-gb675b421 (https://github.com/astroidmail/astroid) Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 x-cbid: 20040109-0028-0000-0000-000003EFF165 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20040109-0029-0000-0000-000024B576E8 Message-Id: <1585734073.0qmf6bbdoa.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.676 definitions=2020-03-31_07:2020-03-31, 2020-03-31 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 spamscore=0 impostorscore=0 phishscore=0 priorityscore=1501 lowpriorityscore=0 mlxlogscore=999 bulkscore=0 suspectscore=0 adultscore=0 mlxscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004010078 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Gautham, Gautham R. Shenoy wrote: > From: "Gautham R. Shenoy" >=20 > Currently when CPU goes idle, we take a snapshot of PURR via > pseries_idle_prolog() which is used at the CPU idle exit to compute > the idle PURR cycles via the function pseries_idle_epilog(). Thus, > the value of idle PURR cycle thus read before pseries_idle_prolog() and > after pseries_idle_epilog() is always correct. >=20 > However, if we were to read the idle PURR cycles from an interrupt > context between pseries_idle_prolog() and pseries_idle_epilog() (this wil= l > be done in a future patch), then, the value of the idle PURR thus read > will not include the cycles spent in the most recent idle period. >=20 > This patch addresses the issue by providing accessor function to read > the idle PURR such such that it includes the cycles spent in the most > recent idle period, if we read it between pseries_idle_prolog() and > pseries_idle_epilog(). In order to achieve it, the patch saves the > snapshot of PURR in pseries_idle_prolog() in a per-cpu variable, > instead of on the stack, so that it can be accessed from an interrupt > context. >=20 > Signed-off-by: Gautham R. Shenoy > --- > arch/powerpc/include/asm/idle.h | 47 +++++++++++++++++++++++++++-= ------ > arch/powerpc/platforms/pseries/setup.c | 7 +++-- > drivers/cpuidle/cpuidle-pseries.c | 15 +++++------ > 3 files changed, 47 insertions(+), 22 deletions(-) >=20 > diff --git a/arch/powerpc/include/asm/idle.h b/arch/powerpc/include/asm/i= dle.h > index 32064a4c..d4bfb6a 100644 > --- a/arch/powerpc/include/asm/idle.h > +++ b/arch/powerpc/include/asm/idle.h > @@ -5,10 +5,27 @@ > #include >=20 > #ifdef CONFIG_PPC_PSERIES > -static inline void pseries_idle_prolog(unsigned long *in_purr) > +DECLARE_PER_CPU(u64, idle_entry_purr_snap); > + > +static inline void snapshot_purr_idle_entry(void) > +{ > + *this_cpu_ptr(&idle_entry_purr_snap) =3D mfspr(SPRN_PURR); > +} > + > +static inline void update_idle_purr_accounting(void) > +{ > + u64 wait_cycles; > + u64 in_purr =3D *this_cpu_ptr(&idle_entry_purr_snap); > + > + wait_cycles =3D be64_to_cpu(get_lppaca()->wait_state_cycles); > + wait_cycles +=3D mfspr(SPRN_PURR) - in_purr; > + get_lppaca()->wait_state_cycles =3D cpu_to_be64(wait_cycles); > +} > + > +static inline void pseries_idle_prolog(void) > { > ppc64_runlatch_off(); > - *in_purr =3D mfspr(SPRN_PURR); > + snapshot_purr_idle_entry(); > /* > * Indicate to the HV that we are idle. Now would be > * a good time to find other work to dispatch. > @@ -16,16 +33,28 @@ static inline void pseries_idle_prolog(unsigned long = *in_purr) > get_lppaca()->idle =3D 1; > } >=20 > -static inline void pseries_idle_epilog(unsigned long in_purr) > +static inline void pseries_idle_epilog(void) > { > - u64 wait_cycles; > - > - wait_cycles =3D be64_to_cpu(get_lppaca()->wait_state_cycles); > - wait_cycles +=3D mfspr(SPRN_PURR) - in_purr; > - get_lppaca()->wait_state_cycles =3D cpu_to_be64(wait_cycles); > + update_idle_purr_accounting(); > get_lppaca()->idle =3D 0; > - > ppc64_runlatch_on(); > } > + > +static inline u64 read_this_idle_purr(void) > +{ > + /* > + * If we are reading from an idle context, update the > + * idle-purr cycles corresponding to the last idle period. > + * Since the idle context is not yet over, take a fresh > + * snapshot of the idle-purr. > + */ > + if (unlikely(get_lppaca()->idle =3D=3D 1)) { > + update_idle_purr_accounting(); > + snapshot_purr_idle_entry(); > + } > + > + return be64_to_cpu(get_lppaca()->wait_state_cycles); > +} > + I think this and read_this_idle_spurr() from the next patch should be=20 moved to Patch 4/6, where they are actually used. - Naveen