From: Walker, Benjamin <benjamin.walker at intel.com>
To: spdk@lists.01.org
Subject: Re: [SPDK] NBD with SPDK
Date: Wed, 04 Sep 2019 18:08:21 +0000 [thread overview]
Message-ID: <ab7ff3c981b1b00326d04301d93c5bede1af7a66.camel@intel.com> (raw)
In-Reply-To: E1CEF699-17E8-49B2-B48D-7E3C437B4971@ebay.com
[-- Attachment #1: Type: text/plain, Size: 10123 bytes --]
On Fri, 2019-08-30 at 22:28 +0000, Mittal, Rishabh wrote:
> I got the run again. It is with 4k write.
>
> 13.16% vhost [.]
> spdk_ring_dequeue
>
> 6.08% vhost [.]
> rte_rdtsc
>
> 4.77% vhost [.]
> spdk_thread_poll
>
> 2.85% vhost [.]
> _spdk_reactor_run
>
You're doing high queue depth for at least 30 seconds while the trace runs,
right? Using fio with the libaio engine on the NBD device is probably the way to
go. Are you limiting the profiling to just the core where the main SPDK process
is pinned? I'm asking because SPDK still appears to be mostly idle, and I
suspect the time is being spent in some other thread (in the kernel). Consider
capturing a profile for the entire system. It will have fio stuff in it, but the
expensive stuff still should generally bubble up to the top.
Thanks,
Ben
>
> On 8/29/19, 6:05 PM, "Mittal, Rishabh" <rimittal(a)ebay.com> wrote:
>
> I got the profile with first run.
>
> 27.91% vhost [.]
> spdk_ring_dequeue
>
> 12.94% vhost [.]
> rte_rdtsc
>
> 11.00% vhost [.]
> spdk_thread_poll
>
> 6.15% vhost [.]
> _spdk_reactor_run
>
> 4.35% [kernel] [k]
> syscall_return_via_sysret
>
> 3.91% vhost [.]
> _spdk_msg_queue_run_batch
>
> 3.38% vhost [.]
> _spdk_event_queue_run_batch
>
> 2.83% [unknown] [k]
> 0xfffffe000000601b
>
> 1.45% vhost [.]
> spdk_thread_get_from_ctx
>
> 1.20% [kernel] [k]
> __fget
>
> 1.14% libpthread-2.27.so [.]
> __libc_read
>
> 1.00% libc-2.27.so [.]
> 0x000000000018ef76
>
> 0.99% libc-2.27.so [.] 0x000000000018ef79
>
> Thanks
> Rishabh Mittal
>
> On 8/19/19, 7:42 AM, "Luse, Paul E" <paul.e.luse(a)intel.com> wrote:
>
> That's great. Keep any eye out for the items Ben mentions below - at
> least the first one should be quick to implement and compare both profile data
> and measured performance.
>
> Don’t' forget about the community meetings either, great place to chat
> about these kinds of things.
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fspdk.io%2Fcommunity%2F&data=02%7C01%7Crimittal%40ebay.com%7Cd5c75891ea414963501c08d724b36248%7C46326bff992841a0baca17c16c94ea99%7C0%7C0%7C637018225183900855&sdata=wEMi40AMPeGVt3XX3bHfneHqM0LFEB8Jt%2F9dQl6cIBE%3D&reserved=0
> Next one is tomorrow morn US time.
>
> Thx
> Paul
>
> -----Original Message-----
> From: SPDK [mailto:spdk-bounces(a)lists.01.org] On Behalf Of Mittal,
> Rishabh via SPDK
> Sent: Thursday, August 15, 2019 6:50 PM
> To: Harris, James R <james.r.harris(a)intel.com>; Walker, Benjamin <
> benjamin.walker(a)intel.com>; spdk(a)lists.01.org
> Cc: Mittal, Rishabh <rimittal(a)ebay.com>; Chen, Xiaoxi <
> xiaoxchen(a)ebay.com>; Szmyd, Brian <bszmyd(a)ebay.com>; Kadayam, Hari <
> hkadayam(a)ebay.com>
> Subject: Re: [SPDK] NBD with SPDK
>
> Thanks. I will get the profiling by next week.
>
> On 8/15/19, 6:26 PM, "Harris, James R" <james.r.harris(a)intel.com>
> wrote:
>
>
>
> On 8/15/19, 4:34 PM, "Mittal, Rishabh" <rimittal(a)ebay.com> wrote:
>
> Hi Jim
>
> What tool you use to take profiling.
>
> Hi Rishabh,
>
> Mostly I just use "perf top".
>
> -Jim
>
>
> Thanks
> Rishabh Mittal
>
> On 8/14/19, 9:54 AM, "Harris, James R" <
> james.r.harris(a)intel.com> wrote:
>
>
>
> On 8/14/19, 9:18 AM, "Walker, Benjamin" <
> benjamin.walker(a)intel.com> wrote:
>
> <trim>
>
> When an I/O is performed in the process initiating the
> I/O to a file, the data
> goes into the OS page cache buffers at a layer far
> above the bio stack
> (somewhere up in VFS). If SPDK were to reserve some
> memory and hand it off to
> your kernel driver, your kernel driver would still
> need to copy it to that
> location out of the page cache buffers. We can't
> safely share the page cache
> buffers with a user space process.
>
> I think Rishabh was suggesting the SPDK reserve the
> virtual address space only.
> Then the kernel could map the page cache buffers into that
> virtual address space.
> That would not require a data copy, but would require the
> mapping operations.
>
> I think the profiling data would be really helpful - to
> quantify how much of the 50us
> Is due to copying the 4KB of data. That can help drive
> next steps on how to optimize
> the SPDK NBD module.
>
> Thanks,
>
> -Jim
>
>
> As Paul said, I'm skeptical that the memcpy is
> significant in the overall
> performance you're measuring. I encourage you to go
> look at some profiling data
> and confirm that the memcpy is really showing up. I
> suspect the overhead is
> instead primarily in these spots:
>
> 1) Dynamic buffer allocation in the SPDK NBD backend.
>
> As Paul indicated, the NBD target is dynamically
> allocating memory for each I/O.
> The NBD backend wasn't designed to be fast - it was
> designed to be simple.
> Pooling would be a lot faster and is something fairly
> easy to implement.
>
> 2) The way SPDK does the syscalls when it implements
> the NBD backend.
>
> Again, the code was designed to be simple, not high
> performance. It simply calls
> read() and write() on the socket for each command.
> There are much higher
> performance ways of doing this, they're just more
> complex to implement.
>
> 3) The lack of multi-queue support in NBD
>
> Every I/O is funneled through a single sockpair up to
> user space. That means
> there is locking going on. I believe this is just a
> limitation of NBD today - it
> doesn't plug into the block-mq stuff in the kernel and
> expose multiple
> sockpairs. But someone more knowledgeable on the
> kernel stack would need to take
> a look.
>
> Thanks,
> Ben
>
> >
> > Couple of things that I am not really sure in this
> flow is :- 1. How memory
> > registration is going to work with RDMA driver.
> > 2. What changes are required in spdk memory
> management
> >
> > Thanks
> > Rishabh Mittal
>
>
>
>
>
>
>
>
> _______________________________________________
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> SPDK(a)lists.01.org
>
> https://nam01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flists.01.org%2Fmailman%2Flistinfo%2Fspdk&data=02%7C01%7Crimittal%40ebay.com%7Cd5c75891ea414963501c08d724b36248%7C46326bff992841a0baca17c16c94ea99%7C0%7C0%7C637018225183900855&sdata=9QDXP2O4MWvrQmKitBJONSkZZHXrRqfFXPrDqltPYjM%3D&reserved=0
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>
>
>
next reply other threads:[~2019-09-04 18:08 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-04 18:08 Walker, Benjamin [this message]
-- strict thread matches above, loose matches on Subject: below --
2019-09-23 1:03 [SPDK] NBD with SPDK Huang Zhiteng
2019-09-06 20:31 Kadayam, Hari
2019-09-06 17:13 Mittal, Rishabh
2019-09-06 2:14 Szmyd, Brian
2019-09-06 2:08 Huang Zhiteng
2019-09-05 22:00 Szmyd, Brian
2019-09-05 21:22 Walker, Benjamin
2019-09-05 20:11 Luse, Paul E
2019-09-04 23:27 Luse, Paul E
2019-09-04 23:03 Luse, Paul E
2019-08-30 22:28 Mittal, Rishabh
2019-08-30 17:06 Walker, Benjamin
2019-08-30 1:05 Mittal, Rishabh
2019-08-19 14:41 Luse, Paul E
2019-08-16 1:50 Mittal, Rishabh
2019-08-16 1:26 Harris, James R
2019-08-15 23:34 Mittal, Rishabh
2019-08-14 17:55 Mittal, Rishabh
2019-08-14 17:05 Kadayam, Hari
2019-08-14 16:54 Harris, James R
2019-08-14 16:18 Walker, Benjamin
2019-08-14 14:28 Luse, Paul E
2019-08-13 22:08 Mittal, Rishabh
2019-08-13 21:45 Harris, James R
2019-08-13 19:55 Mittal, Rishabh
2019-08-12 18:41 Harris, James R
2019-08-12 18:11 Harris, James R
2019-08-11 23:33 Mittal, Rishabh
2019-08-11 22:51 Mittal, Rishabh
2019-08-11 19:53 Luse, Paul E
2019-08-11 1:08 Mittal, Rishabh
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