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Fri, 22 Mar 2019 22:10:32 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserv0022.oracle.com (8.14.4/8.14.4) with ESMTP id x2MMAVOT021335 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 22 Mar 2019 22:10:32 GMT Received: from abhmp0015.oracle.com (abhmp0015.oracle.com [141.146.116.21]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x2MMAVao027854; Fri, 22 Mar 2019 22:10:31 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Fri, 22 Mar 2019 15:10:31 -0700 Subject: Re: [PATCH] x86/xen: Add "xen_timer_slop" command line option To: thibodux@gmail.com, xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org Cc: oleksandr_andrushchenko@epam.com, tglx@linutronix.de, jgross@suse.com, ryan.thibodeaux@starlab.io References: <1553279397-130201-1-git-send-email-ryan.thibodeaux@starlab.io> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <1553279397-130201-1-git-send-email-ryan.thibodeaux@starlab.io> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9203 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1011 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-1903220157 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/22/19 2:29 PM, thibodux@gmail.com wrote: > From: Ryan Thibodeaux > > Add a new command-line option "xen_timer_slop=" that sets the > minimum delta of virtual Xen timers. This commit does not change the > default timer slop value for virtual Xen timers. > > Lowering the timer slop value should improve the accuracy of virtual > timers (e.g., better process dispatch latency), but it will likely > increase the number of virtual timer interrupts (relative to the > original slop setting). > > The original timer slop value has not changed since the introduction > of the Xen-aware Linux kernel code. This commit provides users an > opportunity to tune timer performance given the refinements to > hardware and the Xen event channel processing. It also mirrors > a feature in the Xen hypervisor - the "timer_slop" Xen command line > option. Is there any data that shows effects of using this new parameter? -boris > > Signed-off-by: Ryan Thibodeaux > --- > Documentation/admin-guide/kernel-parameters.txt | 7 +++++++ > arch/x86/xen/time.c | 18 ++++++++++++++++-- > 2 files changed, 23 insertions(+), 2 deletions(-) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 858b6c0..fb58c84 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -5129,6 +5129,13 @@ > with /sys/devices/system/xen_memory/xen_memory0/scrub_pages. > Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT. > > + xen_timer_slop= [X86-64,XEN] > + Set the timer slop (in nanoseconds) for the virtual Xen > + timers (default is 100000). This adjusts the minimum > + delta of virtualized Xen timers, where lower values > + improve timer resolution at the expense of processing > + more timer interrupts. > + > xirc2ps_cs= [NET,PCMCIA] > Format: > ,,,,,[,[,[,]]] > diff --git a/arch/x86/xen/time.c b/arch/x86/xen/time.c > index 6e29794..0393968 100644 > --- a/arch/x86/xen/time.c > +++ b/arch/x86/xen/time.c > @@ -212,7 +212,7 @@ static int xen_timerop_set_next_event(unsigned long delta, > return 0; > } > > -static const struct clock_event_device xen_timerop_clockevent = { > +static struct clock_event_device xen_timerop_clockevent __ro_after_init = { > .name = "xen", > .features = CLOCK_EVT_FEAT_ONESHOT, > > @@ -273,7 +273,7 @@ static int xen_vcpuop_set_next_event(unsigned long delta, > return ret; > } > > -static const struct clock_event_device xen_vcpuop_clockevent = { > +static struct clock_event_device xen_vcpuop_clockevent __ro_after_init = { > .name = "xen", > .features = CLOCK_EVT_FEAT_ONESHOT, > > @@ -570,3 +570,17 @@ void __init xen_hvm_init_time_ops(void) > x86_platform.set_wallclock = xen_set_wallclock; > } > #endif > + > +/* Kernel parameter to specify Xen timer slop */ > +static int __init parse_xen_timer_slop(char *ptr) > +{ > + unsigned long slop = memparse(ptr, NULL); > + > + xen_timerop_clockevent.min_delta_ns = slop; > + xen_timerop_clockevent.min_delta_ticks = slop; > + xen_vcpuop_clockevent.min_delta_ns = slop; > + xen_vcpuop_clockevent.min_delta_ticks = slop; > + > + return 0; > +} > +early_param("xen_timer_slop", parse_xen_timer_slop);