From: Ritesh Harjani (IBM) <ritesh.list@gmail•com>
To: Christophe Leroy <christophe.leroy@csgroup•eu>,
linuxppc-dev@lists•ozlabs.org
Cc: Madhavan Srinivasan <maddy@linux•ibm.com>,
Michael Ellerman <mpe@ellerman•id.au>,
Nicholas Piggin <npiggin@gmail•com>,
Paul Mackerras <paulus@ozlabs•org>,
"Aneesh Kumar K.V" <aneesh.kumar@kernel•org>,
Donet Tom <donettom@linux•ibm.com>
Subject: Re: [RFC 7/8] powerpc/book3s64/slb: Add no_slb_preload early cmdline param
Date: Sat, 30 Aug 2025 15:41:44 +0530 [thread overview]
Message-ID: <87qzwtjezj.fsf@gmail.com> (raw)
In-Reply-To: <70d03b12-86a9-4f6b-bbec-334cfd439e26@csgroup.eu>
Christophe Leroy <christophe.leroy@csgroup•eu> writes:
> Le 30/08/2025 à 05:51, Ritesh Harjani (IBM) a écrit :
>> no_slb_preload cmdline can come useful in quickly disabling and/or
>> testing the performance impact of userspace slb preloads. Recently there
>> was a slb multi-hit issue due to slb preload cache which was very
>> difficult to triage. This cmdline option allows to quickly disable
>> preloads and verify if the issue exists in preload cache or somewhere
>> else. This can also be a useful option to see the effect of slb preloads
>> for any application workload e.g. number of slb faults with or w/o slb
>> preloads.
>>
>> For e.g. with the next patch where we added slb_faults counter to /proc/vmstat:
>>
>> with slb_preload:
>> slb_faults (minimal initrd boot): 15
>> slb_faults (full systemd boot): 300
>>
>> with no_slb_preload:
>> slb_faults (minimal initrd boot): 33
>> slb_faults (full systemd boot): 138180
>>
>> Cc: Madhavan Srinivasan <maddy@linux•ibm.com>
>> Cc: Michael Ellerman <mpe@ellerman•id.au>
>> Cc: Nicholas Piggin <npiggin@gmail•com>
>> Cc: Christophe Leroy <christophe.leroy@csgroup•eu>
>> Cc: Paul Mackerras <paulus@ozlabs•org>
>> Cc: "Aneesh Kumar K.V" <aneesh.kumar@kernel•org>
>> Cc: Donet Tom <donettom@linux•ibm.com>
>> Cc: linuxppc-dev@lists•ozlabs.org
>> Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail•com>
>> ---
>> Documentation/admin-guide/kernel-parameters.txt | 3 +++
>> arch/powerpc/mm/book3s64/hash_utils.c | 3 +++
>> arch/powerpc/mm/book3s64/internal.h | 7 +++++++
>> arch/powerpc/mm/book3s64/slb.c | 15 +++++++++++++++
>> 4 files changed, 28 insertions(+)
>>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 747a55abf494..9a66f255b659 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -7135,6 +7135,9 @@
>> them frequently to increase the rate of SLB faults
>> on kernel addresses.
>>
>> + no_slb_preload [PPC,EARLY]
>> + Disables slb preloading for userspace.
>> +
>> sunrpc.min_resvport=
>> sunrpc.max_resvport=
>> [NFS,SUNRPC]
>> diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
>> index 495b6da6f5d4..abf703563ea3 100644
>> --- a/arch/powerpc/mm/book3s64/hash_utils.c
>> +++ b/arch/powerpc/mm/book3s64/hash_utils.c
>> @@ -1319,6 +1319,9 @@ static void __init htab_initialize(void)
>> if (stress_slb_enabled)
>> static_branch_enable(&stress_slb_key);
>>
>> + if (no_slb_preload)
>> + static_branch_enable(&no_slb_preload_key);
>> +
>> if (stress_hpt_enabled) {
>> unsigned long tmp;
>> static_branch_enable(&stress_hpt_key);
>> diff --git a/arch/powerpc/mm/book3s64/internal.h b/arch/powerpc/mm/book3s64/internal.h
>> index c26a6f0c90fc..cad08d83369c 100644
>> --- a/arch/powerpc/mm/book3s64/internal.h
>> +++ b/arch/powerpc/mm/book3s64/internal.h
>> @@ -22,6 +22,13 @@ static inline bool stress_hpt(void)
>> return static_branch_unlikely(&stress_hpt_key);
>> }
>>
>> +extern bool no_slb_preload;
>> +DECLARE_STATIC_KEY_FALSE(no_slb_preload_key);
>> +static inline bool slb_preload_disabled(void)
>> +{
>> + return static_branch_unlikely(&no_slb_preload_key);
>> +}
>> +
>> void hpt_do_stress(unsigned long ea, unsigned long hpte_group);
>>
>> void exit_lazy_flush_tlb(struct mm_struct *mm, bool always_flush);
>> diff --git a/arch/powerpc/mm/book3s64/slb.c b/arch/powerpc/mm/book3s64/slb.c
>> index 780792b9a1e5..297ab0e93c1e 100644
>> --- a/arch/powerpc/mm/book3s64/slb.c
>> +++ b/arch/powerpc/mm/book3s64/slb.c
>> @@ -42,6 +42,15 @@ early_param("stress_slb", parse_stress_slb);
>>
>> __ro_after_init DEFINE_STATIC_KEY_FALSE(stress_slb_key);
>>
>> +bool no_slb_preload __initdata;
>> +static int __init parse_no_slb_preload(char *p)
>> +{
>> + no_slb_preload = true;
>> + return 0;
>
> Can't you call static_branch_disable() directly from here and avoid
> doing it in hash_utils.c ?
>
parse_early_param() for cmdline options happens before the setup_feature_keys().
Hence we cannot call static_branch_disable() here in parse_no_slb_preload()
-ritesh
next prev parent reply other threads:[~2025-08-30 10:14 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-30 3:51 [PATCH 0/8] powerpc/book3s64: Hash / SLB fixes & improvements Ritesh Harjani (IBM)
2025-08-30 3:51 ` [RFC 1/8] powerpc/mm: Fix SLB multihit issue during SLB preload Ritesh Harjani (IBM)
2025-08-30 3:51 ` [RFC 2/8] book3s64/hash: Restrict stress_hpt_struct memblock region to within RMA limit Ritesh Harjani (IBM)
2025-08-30 3:51 ` [RFC 3/8] book3s64/hash: Fix phys_addr_t printf format in htab_initialize() Ritesh Harjani (IBM)
2025-08-30 6:26 ` Christophe Leroy
2025-08-30 7:30 ` Ritesh Harjani
2025-08-30 3:51 ` [RFC 4/8] powerpc/ptdump/64: Fix kernel_hash_pagetable dump for ISA v3.00 HPTE format Ritesh Harjani (IBM)
2025-08-30 3:51 ` [RFC 5/8] powerpc/ptdump: Dump PXX level info for kernel_page_tables Ritesh Harjani (IBM)
2025-08-30 6:31 ` Christophe Leroy
2025-08-30 7:25 ` Ritesh Harjani
2025-08-30 3:51 ` [RFC 6/8] powerpc/book3s64/slb: Make preload_add return type as void Ritesh Harjani (IBM)
2025-08-30 6:36 ` Christophe Leroy
2025-08-30 7:27 ` Ritesh Harjani
2025-08-30 3:51 ` [RFC 7/8] powerpc/book3s64/slb: Add no_slb_preload early cmdline param Ritesh Harjani (IBM)
2025-08-30 6:42 ` Christophe Leroy
2025-08-30 10:11 ` Ritesh Harjani [this message]
2025-08-30 3:51 ` [RFC 8/8] powerpc/book3s64/slb: Add slb faults to vmstat Ritesh Harjani (IBM)
2025-08-30 4:45 ` Stephen Rothwell
2025-08-30 4:56 ` Ritesh Harjani
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