From: Amos Kong <akong@redhat.com>
To: "Michael Büsch" <m@bues.ch>
Cc: virtualization@lists.linux-foundation.org, kvm@vger.kernel.org,
herbert@gondor.apana.org.au, mpm@selenic.com,
rusty@rustcorp.com.au, amit.shah@redhat.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 3/3] hw_random: increase schedule timeout in rng_dev_read()
Date: Tue, 16 Sep 2014 08:27:40 +0800 [thread overview]
Message-ID: <20140916002740.GA5671@zen> (raw)
In-Reply-To: <20140915181331.4e3f5fed@wiggum>
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On Mon, Sep 15, 2014 at 06:13:31PM +0200, Michael Büsch wrote:
> On Tue, 16 Sep 2014 00:02:29 +0800
> Amos Kong <akong@redhat.com> wrote:
>
> > This patch increases the schedule timeout to 10 jiffies, it's more
> > appropriate, then other takes can easy to hold the mutex lock.
> >
> > Signed-off-by: Amos Kong <akong@redhat.com>
> > ---
> > drivers/char/hw_random/core.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c
> > index 263a370..b5d1b6f 100644
> > --- a/drivers/char/hw_random/core.c
> > +++ b/drivers/char/hw_random/core.c
> > @@ -195,7 +195,7 @@ static ssize_t rng_dev_read(struct file *filp, char __user *buf,
> >
> > mutex_unlock(&rng_mutex);
> >
> > - schedule_timeout_interruptible(1);
> > + schedule_timeout_interruptible(10);
> >
> > if (signal_pending(current)) {
> > err = -ERESTARTSYS;
>
> Does a schedule of 1 ms or 10 ms decrease the throughput?
In my test environment, 1 jiffe always works (100%), as suggested by
Amit 10 jiffes is more appropriate.
After applied current 3 patches, there is a throughput regression.
1.2 M/s -> 6 K/s
We can only schedule in the end of loop (size == 0), and only for
non-smp guest. So smp guest won't be effected.
| if (!size && num_online_cpus() == 1)
| schedule_timeout_interruptible(timeout);
Set timeout to 1:
non-smp guest with quick backend (1.2M/s) -> about 49K/s)
Set timeout to 10:
non-smp guest with quick backend (1.2M/s) -> about 490K/s)
We might need other benchmark to test the performance, but we can
see the bug clearly caused a regression.
As we discussed in other thread, need_resched() should work in this
case, so those patches might be wrong fixing.
> I think we need some benchmarks.
>
> --
> Michael
--
Amos.
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next prev parent reply other threads:[~2014-09-16 0:29 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-15 16:02 [PATCH v2 0/3] fix stuck in accessing hwrng attributes Amos Kong
2014-09-15 16:02 ` [PATCH v2 1/3] virtio-rng cleanup: move some code out of mutex protection Amos Kong
2014-09-15 16:13 ` Michael Büsch
2014-09-16 0:30 ` Amos Kong
2014-09-15 16:02 ` [PATCH v2 2/3] hw_random: fix stuck in catting hwrng attributes Amos Kong
2014-09-18 2:43 ` Rusty Russell
2014-09-18 2:48 ` [PATCH 1/5] hw_random: place mutex around read functions and buffers Rusty Russell
2014-09-18 2:48 ` [PATCH 2/5] hw_random: use reference counts on each struct hwrng Rusty Russell
2014-09-18 12:22 ` Amos Kong
2014-09-18 2:48 ` [PATCH 3/5] hw_random: fix unregister race Rusty Russell
2014-10-21 14:15 ` Herbert Xu
2014-11-03 15:24 ` Amos Kong
2014-09-18 2:48 ` [PATCH 4/5] hw_random: don't double-check old_rng Rusty Russell
2014-09-18 2:48 ` [PATCH 5/5] hw_random: don't init list element we're about to add to list Rusty Russell
2014-09-18 12:47 ` [PATCH v2 2/3] hw_random: fix stuck in catting hwrng attributes Amos Kong
2014-09-15 16:02 ` [PATCH v2 3/3] hw_random: increase schedule timeout in rng_dev_read() Amos Kong
2014-09-15 16:13 ` Michael Büsch
2014-09-16 0:27 ` Amos Kong [this message]
2014-09-16 15:01 ` Michael Büsch
2014-09-17 9:30 ` [PATCH v2 0/3] fix stuck in accessing hwrng attributes Herbert Xu
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