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From: Jerin Jacob <jerinjacobk@gmail.com>
To: Ruifeng Wang <Ruifeng.Wang@arm.com>
Cc: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>,
	"dev@dpdk.org" <dev@dpdk.org>,
	"jerinj@marvell.com" <jerinj@marvell.com>,
	"hemant.agrawal@nxp.com" <hemant.agrawal@nxp.com>,
	 "Ajit Khaparde (ajit.khaparde@broadcom.com)"
	<ajit.khaparde@broadcom.com>,
	"igorch@amazon.com" <igorch@amazon.com>,
	 "thomas@monjalon.net" <thomas@monjalon.net>,
	"viacheslavo@mellanox.com" <viacheslavo@mellanox.com>,
	 "arybchenko@solarflare.com" <arybchenko@solarflare.com>,
	nd <nd@arm.com>
Subject: Re: [dpdk-dev] [RFC] eal: adjust barriers for IO on Armv8-a
Date: Tue, 12 May 2020 13:58:46 +0530	[thread overview]
Message-ID: <CALBAE1P8JsB=J=B-tSx5Gbvg5L-x63nSFAE0bu2Y83VJLFktcQ@mail.gmail.com> (raw)
In-Reply-To: <HE1PR0801MB202574D9E0E14ADB480460099EBE0@HE1PR0801MB2025.eurprd08.prod.outlook.com>

On Tue, May 12, 2020 at 1:32 PM Ruifeng Wang <Ruifeng.Wang@arm.com> wrote:
>
>
> > -----Original Message-----
> > From: Jerin Jacob <jerinjacobk@gmail.com>
> > Sent: Tuesday, May 12, 2020 2:42 PM
> > To: Ruifeng Wang <Ruifeng.Wang@arm.com>
> > Cc: Honnappa Nagarahalli <Honnappa.Nagarahalli@arm.com>;
> > dev@dpdk.org; jerinj@marvell.com; hemant.agrawal@nxp.com; Ajit
> > Khaparde (ajit.khaparde@broadcom.com) <ajit.khaparde@broadcom.com>;
> > igorch@amazon.com; thomas@monjalon.net; viacheslavo@mellanox.com;
> > arybchenko@solarflare.com; nd <nd@arm.com>
> > Subject: Re: [dpdk-dev] [RFC] eal: adjust barriers for IO on Armv8-a
> >
> > On Tue, May 12, 2020 at 11:48 AM Ruifeng Wang <Ruifeng.Wang@arm.com>
> > wrote:
> > >
> > >
> > > > -----Original Message-----
> > > > From: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > > > Sent: Tuesday, May 12, 2020 2:07 AM
> > > > To: dev@dpdk.org; jerinj@marvell.com; hemant.agrawal@nxp.com; Ajit
> > > > Khaparde (ajit.khaparde@broadcom.com)
> > <ajit.khaparde@broadcom.com>;
> > > > igorch@amazon.com; thomas@monjalon.net;
> > viacheslavo@mellanox.com;
> > > > arybchenko@solarflare.com; Honnappa Nagarahalli
> > > > <Honnappa.Nagarahalli@arm.com>
> > > > Cc: Ruifeng Wang <Ruifeng.Wang@arm.com>; nd <nd@arm.com>
> > > > Subject: [RFC] eal: adjust barriers for IO on Armv8-a
> > > >
> > > > Change the barrier APIs for IO to reflect that Armv8-a is
> > > > other-multi-copy atomicity memory model.
> > > >
> > > > Armv8-a memory model has been strengthened to require
> > > > other-multi-copy atomicity. This property requires memory accesses
> > > > from an observer to become visible to all other observers
> > > > simultaneously [3]. This means
> > > >
> > > > a) A write arriving at an endpoint shared between multiple CPUs is
> > > >    visible to all CPUs
> > > > b) A write that is visible to all CPUs is also visible to all other
> > > >    observers in the shareability domain
> > > >
> > > > This allows for using cheaper DMB instructions in the place of DSB
> > > > for devices that are visible to all CPUs (i.e. devices that DPDK caters to).
> > > >
> > > > Please refer to [1], [2] and [3] for more information.
> > > >
> > > > [1]
> > > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/c
> > > > ommit/?i d=22ec71615d824f4f11d38d0e55a88d8956b7e45f
> > > > [2] https://www.youtube.com/watch?v=i6DayghhA8Q
> > > > [3] https://www.cl.cam.ac.uk/~pes20/armv8-mca/
> > > >
> > > > Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > > > ---
> > > >  lib/librte_eal/arm/include/rte_atomic_64.h | 10 +++++-----
> > > >  1 file changed, 5 insertions(+), 5 deletions(-)
> > > >
> > > > diff --git a/lib/librte_eal/arm/include/rte_atomic_64.h
> > > > b/lib/librte_eal/arm/include/rte_atomic_64.h
> > > > index 7b7099cdc..e406411bb 100644
> > > > --- a/lib/librte_eal/arm/include/rte_atomic_64.h
> > > > +++ b/lib/librte_eal/arm/include/rte_atomic_64.h
> > > > @@ -19,11 +19,11 @@ extern "C" {
> > > >  #include <rte_compat.h>
> > > >  #include <rte_debug.h>
> > > >
> > > > -#define rte_mb() asm volatile("dsb sy" : : : "memory")
> > > > +#define rte_mb() asm volatile("dmb osh" : : : "memory")
> > > >
> > > > -#define rte_wmb() asm volatile("dsb st" : : : "memory")
> > > > +#define rte_wmb() asm volatile("dmb oshst" : : : "memory")
> > > >
> > > > -#define rte_rmb() asm volatile("dsb ld" : : : "memory")
> > > > +#define rte_rmb() asm volatile("dmb oshld" : : : "memory")
> > > >
> > > >  #define rte_smp_mb() asm volatile("dmb ish" : : : "memory")
> > > >
> > > > @@ -37,9 +37,9 @@ extern "C" {
> > > >
> > > >  #define rte_io_rmb() rte_rmb()
> > > >
> > > > -#define rte_cio_wmb() asm volatile("dmb oshst" : : : "memory")
> > > > +#define rte_cio_wmb() rte_wmb()
> > > >
> > > > -#define rte_cio_rmb() asm volatile("dmb oshld" : : : "memory")
> > > > +#define rte_cio_rmb() rte_rmb()
> > > >
> > > >  /*------------------------ 128 bit atomic operations
> > > > -------------------------*/
> > > >
> > > > --
> > > > 2.17.1
> > >
> > > This change showed about 7% performance gain in testpmd single core
> > NDR test.
> >
> > I am trying to understand this patch wrt DPDK current usage model?
> >
> > 1)  Is performance improvement due to the fact that the PMD that you are
> > using it for testing suppose to use existing rte_cio_* but it was using
> > rte_[rw]mb?
>
> This is part of the reason. There are also cases where rte_io_* was used and can be relaxed.
> Such as: http://patches.dpdk.org/patch/68162/
>
> > 2) In my understanding :
> > a) CPU to CPU barrier requirements are addressed by rte_smp_*
> > b) CPU to DMA/Device barrier requirements are addressed by rte_cio_*
> > c) CPU to ANY(CPU or Device) are addressed by  rte_[rw]mb
> >
> > If (c) is true then we are violating the DPDK spec with change. Right?
>
> Developers are still required to use correct barrier APIs for different use cases.
> I think this change mitigates performance penalty when non optimal barrier is used.

But does it violate the contract?  We are using rte_[rw]mb as a low
performance/heavyweight
for all the cases. I think that is the contract to DPDK consumers. For
different requirment,
We have a specific API. IMO, It makes sense to change the fastpath code for more
fine granted barriers based on the need rather than changing the
generic one to lightweight.
i.e rte_[rw]wb is the superset that works on all cases and use
customized one for the specific
use case.

>
> > This change will not be required if fastpath (CPU to Device) is using rte_cio_*.
> > Right?
>
> See 1). Correct usage of rte_cio_* is not the whole.
> For some other use cases, such as barrier between accesses of different memory types, we can also use lighter barrier 'dmb'.
>
> >
> >
> >
> > > Tested-by: Ruifeng Wang <ruifeng.wang@arm.com>
> > >

  reply	other threads:[~2020-05-12  8:29 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-13 12:38 [dpdk-dev] [PATCH RFC v1 0/6] barrier fix and optimization for mlx5 on aarch64 Gavin Hu
2020-02-13 12:38 ` [dpdk-dev] [PATCH RFC v1 1/6] net/mlx5: relax the barrier for UAR write Gavin Hu
2020-02-13 12:38 ` [dpdk-dev] [PATCH RFC v1 2/6] net/mlx5: use cio barrier before the BF WQE Gavin Hu
2020-02-13 12:38 ` [dpdk-dev] [PATCH RFC v1 3/6] net/mlx5: add missing barrier Gavin Hu
2020-02-13 12:38 ` [dpdk-dev] [PATCH RFC v1 4/6] net/mlx5: add descriptive comment for a barrier Gavin Hu
2020-02-13 12:38 ` [dpdk-dev] [PATCH RFC v1 5/6] net/mlx5: non-cacheable mapping defaulted for aarch64 Gavin Hu
2020-02-13 12:38 ` [dpdk-dev] [PATCH RFC v1 6/6] net/mlx5: relaxed ordering for multi-packet RQ buffer refcnt Gavin Hu
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 0/7] introduce new barrier class and use it for mlx5 PMD Gavin Hu
2020-04-10 17:20   ` Andrew Rybchenko
2020-04-11  3:46     ` Gavin Hu
2020-04-13  9:51       ` Andrew Rybchenko
2020-04-13 16:46         ` Gavin Hu
2020-05-11 18:06   ` [dpdk-dev] [RFC] eal: adjust barriers for IO on Armv8-a Honnappa Nagarahalli
2020-05-12  6:18     ` Ruifeng Wang
2020-05-12  6:42       ` Jerin Jacob
2020-05-12  8:02         ` Ruifeng Wang
2020-05-12  8:28           ` Jerin Jacob [this message]
2020-05-12 21:44           ` Honnappa Nagarahalli
2020-05-13 14:49             ` Jerin Jacob
2020-05-14  1:02               ` Honnappa Nagarahalli
2020-06-27 19:12   ` [dpdk-dev] [PATCH v2] " Honnappa Nagarahalli
2020-06-27 19:25     ` Honnappa Nagarahalli
2020-06-30  5:13       ` Jerin Jacob
2020-07-03 18:57   ` [dpdk-dev] [PATCH v3 1/3] " Honnappa Nagarahalli
2020-07-03 18:57     ` [dpdk-dev] [PATCH v3 2/3] doc: update armv8-a IO barrier changes Honnappa Nagarahalli
2020-07-05  0:57       ` Jerin Jacob
2020-07-03 18:57     ` [dpdk-dev] [PATCH v3 3/3] doc: update deprecation of CIO barrier APIs Honnappa Nagarahalli
2020-07-05  0:57       ` Jerin Jacob
2020-07-07 20:19       ` Ajit Khaparde
2020-07-08 11:05       ` Ananyev, Konstantin
2020-07-06 23:43   ` [dpdk-dev] [PATCH v4 1/3] eal: adjust barriers for IO on Armv8-a Honnappa Nagarahalli
2020-07-06 23:43     ` [dpdk-dev] [PATCH v4 2/3] doc: update armv8-a IO barrier changes Honnappa Nagarahalli
2020-07-07  8:36       ` David Marchand
2020-07-07 18:37         ` Honnappa Nagarahalli
2020-07-06 23:43     ` [dpdk-dev] [PATCH v4 3/3] doc: update deprecation of CIO barrier APIs Honnappa Nagarahalli
2020-07-07  8:39       ` David Marchand
2020-07-07 20:14       ` David Christensen
2020-07-08 11:49       ` David Marchand
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 1/7] eal: introduce new class of barriers for DMA use cases Gavin Hu
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 2/7] net/mlx5: dmb for immediate doorbell ring on aarch64 Gavin Hu
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 3/7] net/mlx5: relax barrier to order UAR writes " Gavin Hu
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 4/7] net/mlx5: relax barrier for aarch64 Gavin Hu
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 5/7] net/mlx5: add descriptive comment for a barrier Gavin Hu
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 6/7] net/mlx5: relax ordering for multi-packet RQ buffer refcnt Gavin Hu
2020-06-23  8:26   ` [dpdk-dev] [PATCH v3] net/mlx5: relaxed " Phil Yang
2020-07-13  3:02     ` Phil Yang
2020-07-20 23:21       ` Alexander Kozyrev
2020-07-21  1:55         ` Phil Yang
2020-07-21  3:58           ` Alexander Kozyrev
2020-07-21  4:03             ` Honnappa Nagarahalli
2020-07-21  4:11               ` Alexander Kozyrev
2020-07-22 12:06                 ` Phil Yang
2020-07-23  4:47         ` Honnappa Nagarahalli
2020-07-23  6:11           ` Phil Yang
2020-07-23 16:53             ` Alexander Kozyrev
2020-07-27 14:52               ` Phil Yang
2020-08-06  2:43                 ` Alexander Kozyrev
2020-08-11  5:20                   ` Honnappa Nagarahalli
2020-09-02 21:52                     ` Alexander Kozyrev
2020-09-03  2:55                       ` Phil Yang
2020-09-09 13:29                         ` Alexander Kozyrev
2020-09-10  1:34                           ` Honnappa Nagarahalli
2020-09-03  2:53     ` [dpdk-dev] [PATCH v4] " Phil Yang
2020-09-10  1:30       ` Honnappa Nagarahalli
2020-09-10  1:36         ` Alexander Kozyrev
2020-09-29 15:22           ` Phil Yang
2020-09-30 12:44             ` Slava Ovsiienko
2020-09-30 12:52               ` Raslan Darawsheh
2020-09-30 13:57       ` Raslan Darawsheh
2020-04-10 16:41 ` [dpdk-dev] [PATCH RFC v2 7/7] doc: clarify one configuration in mlx5 guide Gavin Hu

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