Re: [dpdk-dev] [PATCH v3] examples/vhost: fix ioat dependency issue

[Bruce Richardson <bruce.richardson@intel.com>]

On Thu, Nov 12, 2020 at 11:29:56AM +0000, Jiang, Cheng1 wrote:
> Hi Bruce,
> 
> > -----Original Message-----
> > From: Bruce Richardson <bruce.richardson@intel.com>
> > Sent: Thursday, November 12, 2020 6:28 PM
> > To: David Marchand <david.marchand@redhat.com>
> > Cc: Jiang, Cheng1 <cheng1.jiang@intel.com>; Maxime Coquelin
> > <maxime.coquelin@redhat.com>; Xia, Chenbo <chenbo.xia@intel.com>;
> > dev <dev@dpdk.org>; Fu, Patrick <patrick.fu@intel.com>; Yang, YvonneX
> > <yvonnex.yang@intel.com>; Hu, Jiayu <jiayu.hu@intel.com>
> > Subject: Re: [dpdk-dev] [PATCH v3] examples/vhost: fix ioat dependency
> > issue
> >
> > On Thu, Nov 12, 2020 at 10:36:50AM +0100, David Marchand wrote:
> > > On Thu, Nov 12, 2020 at 8:30 AM Cheng Jiang <Cheng1.jiang@intel.com>
> > wrote:
> > > >
> > > > Fix vhost-switch compiling issue when ioat dependency is missing.
> > > > Change 'RTE_x86' check into 'RTE_RAW_IOAT' check in meson build file
> > > > and update Makefile. Clean some codes.
> > > >
> > > > Fixes: abec60e7115d ("examples/vhost: support vhost async data
> > > > path")
> > > > Fixes: 3a04ecb21420 ("examples/vhost: add async vhost args parsing")
> > > >
> > > > Signed-off-by: Cheng Jiang <Cheng1.jiang@intel.com>
> > > > ---
> > > > v3:
> > > >  * Added fixes lines in commit log.
> > > >
> > > > v2:
> > > >  * Cleaned some codes
> > > >  * Changed RTE_RAW_IOAT check method in Makefile
> > > >  * Added ioat function definition when RTE_RAW_IOAT is missing
> > > >
> > > >  examples/vhost/Makefile    |  5 +++++
> > > >  examples/vhost/ioat.h      | 32 +++++++++++++++++++++++++-------
> > > >  examples/vhost/main.c      | 22 +++++++++++-----------
> > > >  examples/vhost/meson.build |  2 +-
> > > >  4 files changed, 42 insertions(+), 19 deletions(-)
> > > >
> > > > diff --git a/examples/vhost/Makefile b/examples/vhost/Makefile index
> > > > cec59d0e0..cbe56f742 100644
> > > > --- a/examples/vhost/Makefile
> > > > +++ b/examples/vhost/Makefile
> > > > @@ -28,6 +28,11 @@ CFLAGS += -O3 $(shell $(PKGCONF) --cflags
> > > > libdpdk)  LDFLAGS_SHARED = $(shell $(PKGCONF) --libs libdpdk)
> > > > LDFLAGS_STATIC = $(shell $(PKGCONF) --static --libs libdpdk)
> > > >
> > > > +HAS_RAW_IOAT=$(shell echo RTE_RAW_IOAT | $(CPP) $(CFLAGS) -P - |
> > > > +tail -1) ifeq ($(HAS_RAW_IOAT), 1) SRCS-y += ioat.c endif
> > > > +
> > > >  CFLAGS += -DALLOW_EXPERIMENTAL_API
> > > >
> > > >  build/$(APP)-shared: $(SRCS-y) Makefile $(PC_FILE) | build
> >
> > <snip>
> >
> > > I'll let Bruce and Maxime have the last word on this patch.
> > > But at least it works for me,
> > > Tested-by: David Marchand <david.marchand@redhat.com>
> > >
> > I don't have a really strong objection to this, but I still would rather see the
> > ioat detection done in the C code only rather than in the Makefile.
> > I'm concerned about us adding too much complexity into our makefiles, so
> > would like to keep them simple as much as possible.
> >
> > Therefore, I'd like to see ioat.c always included in SRCS-y, and ioat.c just have
> > #ifdef RTE_RAW_IOAT to block out any ioat-dependent code.
> >
> > /Bruce
> 
> Tomorrow is the deadline for RC4, it's a little bit rush to prepare a new framework to cover the conditional compiling. Considering we have test efforts and CI check already on-going based on current patch, I would prefer to keep current code structure. Plus, pure C code change could also introduce more readability problem when we have more than one async callback implementations.
>

I don't see any readability problems at all, in fact the result is cleaner
and shorter IMHO - especially the Makefile. I just tested with the
following changes applied on top of your patch, and all seemed to build ok.

Do you see any implementation problems with the below solution?

/Bruce

diff --git a/examples/vhost/Makefile b/examples/vhost/Makefile
index cbe56f742..8c969caaa 100644
--- a/examples/vhost/Makefile
+++ b/examples/vhost/Makefile
@@ -5,7 +5,7 @@
 APP = vhost-switch

 # all source are stored in SRCS-y
-SRCS-y := main.c virtio_net.c
+SRCS-y := main.c virtio_net.c ioat.c

 # Build using pkg-config variables if possible
 ifneq ($(shell pkg-config --exists libdpdk && echo 0),0)
@@ -28,11 +28,6 @@ CFLAGS += -O3 $(shell $(PKGCONF) --cflags libdpdk)
 LDFLAGS_SHARED = $(shell $(PKGCONF) --libs libdpdk)
 LDFLAGS_STATIC = $(shell $(PKGCONF) --static --libs libdpdk)

-HAS_RAW_IOAT=$(shell echo RTE_RAW_IOAT | $(CPP) $(CFLAGS) -P - | tail -1)
-ifeq ($(HAS_RAW_IOAT), 1)
-SRCS-y += ioat.c
-endif
-
 CFLAGS += -DALLOW_EXPERIMENTAL_API

 build/$(APP)-shared: $(SRCS-y) Makefile $(PC_FILE) | build
diff --git a/examples/vhost/ioat.c b/examples/vhost/ioat.c
index b2c74f653..7c1a4f40d 100644
--- a/examples/vhost/ioat.c
+++ b/examples/vhost/ioat.c
@@ -8,6 +8,8 @@
 #include "ioat.h"
 #include "main.h"

+#ifdef RTE_RAW_IOAT
+
 struct dma_for_vhost dma_bind[MAX_VHOST_DEVICE];

 struct packet_tracker {
@@ -199,3 +201,5 @@ ioat_check_completed_copies_cb(int vid, uint16_t queue_id,
        /* Opaque data is not supported */
        return -1;
 }
+
+#endif /* RTE_RAW_IOAT */