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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Wed, 23 Jan 2019 09:10:10 -0000 Received: from d06av22.portsmouth.uk.ibm.com (d06av22.portsmouth.uk.ibm.com [9.149.105.58]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x0N9A98E721238 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Wed, 23 Jan 2019 09:10:09 GMT Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 2BC2F4C04A; Wed, 23 Jan 2019 09:10:09 +0000 (GMT) Received: from d06av22.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0C58E4C050; Wed, 23 Jan 2019 09:10:08 +0000 (GMT) Received: from skywalker.linux.ibm.com (unknown [9.85.69.250]) by d06av22.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 23 Jan 2019 09:10:07 +0000 (GMT) X-Mailer: emacs 26.1 (via feedmail 11-beta-1 I) From: "Aneesh Kumar K.V" To: Michael Ellerman , linuxppc-dev@ozlabs.org Subject: Re: [PATCH 4/4] powerpc/64s: Support shrinking the SLB for debugging In-Reply-To: <20190117121328.13395-4-mpe@ellerman.id.au> References: <20190117121328.13395-1-mpe@ellerman.id.au> <20190117121328.13395-4-mpe@ellerman.id.au> Date: Wed, 23 Jan 2019 14:40:06 +0530 MIME-Version: 1.0 Content-Type: text/plain X-TM-AS-GCONF: 00 x-cbid: 19012309-0028-0000-0000-0000033CEBD0 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19012309-0029-0000-0000-000023FA287F Message-Id: <87va2fbuz5.fsf@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-01-23_05:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1901230071 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: npiggin@gmail.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Michael Ellerman writes: > On machines with 1TB segments and a 32-entry SLB it's quite hard to > cause sufficient SLB pressure to trigger bugs caused due to badly > timed SLB faults. > > We have seen this in the past and a few years ago added the > disable_1tb_segments command line option to force the use of 256MB > segments. However even this allows some bugs to slip through testing > if the SLB entry in question was recently accessed. > > So add a new command line parameter for debugging which shrinks the > SLB to the minimum size we can support. Currently that size is 3, two > bolted SLBs and 1 for dynamic use. This creates the maximal SLB > pressure while still allowing the kernel to operate. > Should we put this within DEBUG_VM? Reviewed-by: Aneesh Kumar K.V > Signed-off-by: Michael Ellerman > --- > arch/powerpc/mm/slb.c | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/powerpc/mm/slb.c b/arch/powerpc/mm/slb.c > index 61450a9cf30d..0f33e28f97da 100644 > --- a/arch/powerpc/mm/slb.c > +++ b/arch/powerpc/mm/slb.c > @@ -506,10 +506,24 @@ void switch_slb(struct task_struct *tsk, struct mm_struct *mm) > asm volatile("isync" : : : "memory"); > } > > +static bool shrink_slb = false; > + > +static int __init parse_shrink_slb(char *p) > +{ > + shrink_slb = true; > + slb_set_size(0); Why do we need call slb_set_size(0) here? htab_dt_scan_seg_sizes should find the shirnk_slb = true? > + > + return 0; > +} > +early_param("shrink_slb", parse_shrink_slb); > + > static u32 slb_full_bitmap; > > void slb_set_size(u16 size) > { > + if (shrink_slb) > + size = SLB_NUM_BOLTED + 1; > + > mmu_slb_size = size; > > if (size >= 32) > -- > 2.20.1 -aneesh