| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <878rjakh22.fsf@mpe.ellerman.id.au>
Date: Wed, 14 Dec 2022 10:41:25 +1100
From: Michael Ellerman <mpe@...erman.id.au>
To: Phil Auld <pauld@...hat.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: Vishal Chourasia <vishalc@...ux.vnet.ibm.com>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org, mingo@...hat.com,
vincent.guittot@...aro.org, vschneid@...hat.com,
srikar@...ux.vnet.ibm.com, sshegde@...ux.ibm.com,
linuxppc-dev@...ts.ozlabs.org, ritesh.list@...il.com,
aneesh.kumar@...ux.ibm.com
Subject: Re: sched/debug: CPU hotplug operation suffers in a large cpu systems
Phil Auld <pauld@...hat.com> writes:
> On Tue, Dec 13, 2022 at 07:23:54AM +0100 Greg Kroah-Hartman wrote:
>> On Mon, Dec 12, 2022 at 02:17:58PM -0500, Phil Auld wrote:
>> > Hi,
>> >
>> > On Tue, Nov 08, 2022 at 01:24:39PM +0100 Greg Kroah-Hartman wrote:
>> > > On Tue, Nov 08, 2022 at 03:30:46PM +0530, Vishal Chourasia wrote:
>> > > >
>> > > > Thanks Greg & Peter for your direction.
>> > > >
>> > > > While we pursue the idea of having debugfs based on kernfs, we thought about
>> > > > having a boot time parameter which would disable creating and updating of the
>> > > > sched_domain debugfs files and this would also be useful even when the kernfs
>> > > > solution kicks in, as users who may not care about these debugfs files would
>> > > > benefit from a faster CPU hotplug operation.
>> > >
>> > > Ick, no, you would be adding a new user/kernel api that you will be
>> > > required to support for the next 20+ years. Just to get over a
>> > > short-term issue before you solve the problem properly.
>> >
>> > I'm not convinced moving these files from debugfs to kernfs is the right
>> > fix. That will take it from ~50 back to ~20 _minutes_ on these systems.
>> > I don't think either of those numbers is reasonable.
>> >
>> > The issue as I see it is the full rebuild for every change with no way to
>> > batch the changes. How about something like the below?
>> >
>> > This puts the domains/* files under the sched_verbose flag. About the only
>> > thing under that flag now are the detailed topology discovery printks anyway
>> > so this fits together nicely.
>> >
>> > This way the files would be off by default (assuming you don't boot with
>> > sched_verbose) and can be created at runtime by enabling verbose. Multiple
>> > changes could also be batched by disabling/makeing changes/re-enabling.
>> >
>> > It does not create a new API, uses one that is already there.
>>
>> The idea seems good, the implementation might need a bit of work :)
>
> More than the one comment below? Let me know.
>
>>
>> > > If you really do not want these debugfs files, just disable debugfs from
>> > > your system. That should be a better short-term solution, right?
>> >
>> > We do find these files useful at times for debugging issue and looking
>> > at what's going on on the system.
>> >
>> > >
>> > > Or better yet, disable SCHED_DEBUG, why can't you do that?
>> >
>> > Same with this... useful information with (modulo issues like this)
>> > small cost. There are also tuning knobs that are only available
>> > with SCHED_DEBUG.
>> >
>> >
>> > Cheers,
>> > Phil
>> >
>> > ---------------
>> >
>> > sched/debug: Put sched/domains files under verbose flag
>> >
>> > The debug files under sched/domains can take a long time to regenerate,
>> > especially when updates are done one at a time. Move these files under
>> > the verbose debug flag. Allow changes to verbose to trigger generation
>> > of the files. This lets a user batch the updates but still have the
>> > information available. The detailed topology printk messages are also
>> > under verbose.
>> >
>> > Signed-off-by: Phil Auld <pauld@...hat.com>
>> > ---
>> > kernel/sched/debug.c | 68 ++++++++++++++++++++++++++++++++++++++++++--
>> > 1 file changed, 66 insertions(+), 2 deletions(-)
>> >
>> > diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
>> > index 1637b65ba07a..2eb51ee3ccab 100644
>> > --- a/kernel/sched/debug.c
>> > +++ b/kernel/sched/debug.c
>> > @@ -280,6 +280,31 @@ static const struct file_operations sched_dynamic_fops = {
>> >
>> > __read_mostly bool sched_debug_verbose;
>> >
>> > +static ssize_t sched_verbose_write(struct file *filp, const char __user *ubuf,
>> > + size_t cnt, loff_t *ppos);
>> > +
>> > +static int sched_verbose_show(struct seq_file *m, void *v)
>> > +{
>> > + if (sched_debug_verbose)
>> > + seq_puts(m,"Y\n");
>> > + else
>> > + seq_puts(m,"N\n");
>> > + return 0;
>> > +}
>> > +
>> > +static int sched_verbose_open(struct inode *inode, struct file *filp)
>> > +{
>> > + return single_open(filp, sched_verbose_show, NULL);
>> > +}
>> > +
>> > +static const struct file_operations sched_verbose_fops = {
>> > + .open = sched_verbose_open,
>> > + .write = sched_verbose_write,
>> > + .read = seq_read,
>> > + .llseek = seq_lseek,
>> > + .release = seq_release,
>> > +};
>> > +
>> > static const struct seq_operations sched_debug_sops;
>> >
>> > static int sched_debug_open(struct inode *inode, struct file *filp)
>> > @@ -303,7 +328,7 @@ static __init int sched_init_debug(void)
>> > debugfs_sched = debugfs_create_dir("sched", NULL);
>> >
>> > debugfs_create_file("features", 0644, debugfs_sched, NULL, &sched_feat_fops);
>> > - debugfs_create_bool("verbose", 0644, debugfs_sched, &sched_debug_verbose);
>> > + debugfs_create_file("verbose", 0644, debugfs_sched, NULL, &sched_verbose_fops);
>> > #ifdef CONFIG_PREEMPT_DYNAMIC
>> > debugfs_create_file("preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
>> > #endif
>> > @@ -402,15 +427,23 @@ void update_sched_domain_debugfs(void)
>> > if (!debugfs_sched)
>> > return;
>> >
>> > + if (!sched_debug_verbose)
>> > + return;
>> > +
>> > if (!cpumask_available(sd_sysctl_cpus)) {
>> > if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
>> > return;
>> > cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
>> > }
>> >
>> > - if (!sd_dentry)
>> > + if (!sd_dentry) {
>> > sd_dentry = debugfs_create_dir("domains", debugfs_sched);
>> >
>> > + /* rebuild sd_sysclt_cpus if empty since it gets cleared below */
>> > + if (cpumask_first(sd_sysctl_cpus) >= nr_cpu_ids)
>> > + cpumask_copy(sd_sysctl_cpus, cpu_online_mask);
>> > + }
>> > +
>> > for_each_cpu(cpu, sd_sysctl_cpus) {
>> > struct sched_domain *sd;
>> > struct dentry *d_cpu;
>> > @@ -443,6 +476,37 @@ void dirty_sched_domain_sysctl(int cpu)
>> >
>> > #endif /* CONFIG_SMP */
>> >
>> > +static ssize_t sched_verbose_write(struct file *filp, const char __user *ubuf,
>> > + size_t cnt, loff_t *ppos)
>> > +{
>> > + struct dentry *dentry = filp->f_path.dentry;
>> > + bool orig = sched_debug_verbose;
>> > + bool bv;
>> > + int r;
>> > +
>> > + r = kstrtobool_from_user(ubuf, cnt, &bv);
>> > + if (!r) {
>> > + mutex_lock(&sched_domains_mutex);
>> > + r = debugfs_file_get(dentry);
>> > + if (unlikely(r))
>> > + return r;
>> > + sched_debug_verbose = bv;
>> > + debugfs_file_put(dentry);
>>
>> Why the get/put of the debugfs dentry? for just this single value?
>
> That's what debugfs_file_write_bool() does, which is where I got that since
> that's really what this is doing. I couldn't see a good way to make this
> just call that.
I think you can do it like below? Only lightly tested :)
cheers
diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
index 1637b65ba07a..bc96380cf336 100644
--- a/kernel/sched/debug.c
+++ b/kernel/sched/debug.c
@@ -280,6 +279,42 @@ static const struct file_operations sched_dynamic_fops = {
__read_mostly bool sched_debug_verbose;
+#ifdef CONFIG_SMP
+static struct dentry *sd_dentry;
+
+static ssize_t sched_verbose_write(struct file *filp, const char __user *ubuf,
+ size_t cnt, loff_t *ppos)
+{
+ ssize_t result;
+ bool orig;
+
+ mutex_lock(&sched_domains_mutex);
+
+ orig = sched_debug_verbose;
+ result = debugfs_write_file_bool(filp, ubuf, cnt, ppos);
+
+ if (sched_debug_verbose && !orig)
+ update_sched_domain_debugfs();
+ else if (!sched_debug_verbose && orig) {
+ debugfs_remove(sd_dentry);
+ sd_dentry = NULL;
+ }
+
+ mutex_unlock(&sched_domains_mutex);
+
+ return result;
+}
+#else
+#define sched_verbose_write debugfs_write_file_bool
+#endif
+
+static const struct file_operations sched_verbose_fops = {
+ .read = debugfs_read_file_bool,
+ .write = sched_verbose_write,
+ .open = simple_open,
+ .llseek = default_llseek,
+};
+
static const struct seq_operations sched_debug_sops;
static int sched_debug_open(struct inode *inode, struct file *filp)
@@ -303,7 +338,7 @@ static __init int sched_init_debug(void)
debugfs_sched = debugfs_create_dir("sched", NULL);
debugfs_create_file("features", 0644, debugfs_sched, NULL, &sched_feat_fops);
- debugfs_create_bool("verbose", 0644, debugfs_sched, &sched_debug_verbose);
+ debugfs_create_file_unsafe("verbose", 0644, debugfs_sched, &sched_debug_verbose, &sched_verbose_fops);
#ifdef CONFIG_PREEMPT_DYNAMIC
debugfs_create_file("preempt", 0644, debugfs_sched, NULL, &sched_dynamic_fops);
#endif
@@ -345,7 +380,6 @@ late_initcall(sched_init_debug);
#ifdef CONFIG_SMP
static cpumask_var_t sd_sysctl_cpus;
-static struct dentry *sd_dentry;
static int sd_flags_show(struct seq_file *m, void *v)
{
@@ -402,15 +436,23 @@ void update_sched_domain_debugfs(void)
if (!debugfs_sched)
return;
+ if (!sched_debug_verbose)
+ return;
+
if (!cpumask_available(sd_sysctl_cpus)) {
if (!alloc_cpumask_var(&sd_sysctl_cpus, GFP_KERNEL))
return;
cpumask_copy(sd_sysctl_cpus, cpu_possible_mask);
}
- if (!sd_dentry)
+ if (!sd_dentry) {
sd_dentry = debugfs_create_dir("domains", debugfs_sched);
+ /* rebuild sd_sysclt_cpus if empty since it gets cleared below */
+ if (cpumask_first(sd_sysctl_cpus) >= nr_cpu_ids)
+ cpumask_copy(sd_sysctl_cpus, cpu_online_mask);
+ }
+
for_each_cpu(cpu, sd_sysctl_cpus) {
struct sched_domain *sd;
struct dentry *d_cpu;
Powered by blists - more mailing lists