On Fri, Aug 11, 2023 at 9:21 PM Tyler Retzlaff
<roret...@linux.microsoft.com> wrote:
>
> Inline assembly is not supported for MSVC x64 instead use _mm_prefetch
> and _mm_cldemote intrinsics.
>
> Signed-off-by: Tyler Retzlaff <roret...@linux.microsoft.com>
> Acked-by: Bruce Richardson <bruce.richard...@intel.com>
> Acked-by: Morten Brørup <m...@smartsharesystems.com>
> Acked-by: Konstantin Ananyev <konstantin.v.anan...@yandex.ru>
> ---
> lib/eal/x86/include/rte_prefetch.h | 25 +++++++++++++++++++++----
> 1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/lib/eal/x86/include/rte_prefetch.h
> b/lib/eal/x86/include/rte_prefetch.h
> index 7fd01c4..7a6988e 100644
> --- a/lib/eal/x86/include/rte_prefetch.h
> +++ b/lib/eal/x86/include/rte_prefetch.h
> @@ -9,30 +9,38 @@
> extern "C" {
> #endif
>
> +#include <emmintrin.h>
> +
> #include <rte_compat.h>
> #include <rte_common.h>
> #include "generic/rte_prefetch.h"
>
> +#pragma GCC diagnostic push
> +#pragma GCC diagnostic ignored "-Wcast-qual"
> +
> static inline void rte_prefetch0(const volatile void *p)
> {
> - asm volatile ("prefetcht0 %[p]" : : [p] "m" (*(const volatile char
> *)p));
> + _mm_prefetch((const void *)p, _MM_HINT_T0);
> }
>
Quite surprisingly, this part (exactly) breaks 32bits build in the
vhost library:
ccache cc -Ilib/librte_vhost.a.p -Ilib
-I../../../git/pub/dpdk.org/main/lib -Ilib/vhost
-I../../../git/pub/dpdk.org/main/lib/vhost -I.
-I../../../git/pub/dpdk.org/main -Iconfig
-I../../../git/pub/dpdk.org/main/config -Ilib/eal/include
-I../../../git/pub/dpdk.org/main/lib/eal/include
-Ilib/eal/linux/include
-I../../../git/pub/dpdk.org/main/lib/eal/linux/include
-Ilib/eal/x86/include
-I../../../git/pub/dpdk.org/main/lib/eal/x86/include -Ilib/eal/common
-I../../../git/pub/dpdk.org/main/lib/eal/common -Ilib/eal
-I../../../git/pub/dpdk.org/main/lib/eal -Ilib/kvargs
-I../../../git/pub/dpdk.org/main/lib/kvargs -Ilib/log
-I../../../git/pub/dpdk.org/main/lib/log -Ilib/metrics
-I../../../git/pub/dpdk.org/main/lib/metrics -Ilib/telemetry
-I../../../git/pub/dpdk.org/main/lib/telemetry -Ilib/ethdev
-I../../../git/pub/dpdk.org/main/lib/ethdev -Ilib/net
-I../../../git/pub/dpdk.org/main/lib/net -Ilib/mbuf
-I../../../git/pub/dpdk.org/main/lib/mbuf -Ilib/mempool
-I../../../git/pub/dpdk.org/main/lib/mempool -Ilib/ring
-I../../../git/pub/dpdk.org/main/lib/ring -Ilib/meter
-I../../../git/pub/dpdk.org/main/lib/meter -Ilib/cryptodev
-I../../../git/pub/dpdk.org/main/lib/cryptodev -Ilib/rcu
-I../../../git/pub/dpdk.org/main/lib/rcu -Ilib/hash
-I../../../git/pub/dpdk.org/main/lib/hash -Ilib/pci
-I../../../git/pub/dpdk.org/main/lib/pci -Ilib/dmadev
-I../../../git/pub/dpdk.org/main/lib/dmadev -fdiagnostics-color=always
-D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=c11
-O2 -g -include rte_config.h -Wcast-qual -Wdeprecated -Wformat
-Wformat-nonliteral -Wformat-security -Wmissing-declarations
-Wmissing-prototypes -Wnested-externs -Wold-style-definition
-Wpointer-arith -Wsign-compare -Wstrict-prototypes -Wundef
-Wwrite-strings -Wno-address-of-packed-member -Wno-packed-not-aligned
-Wno-missing-field-initializers -Wno-zero-length-bounds
-Wno-pointer-to-int-cast -D_GNU_SOURCE -m32 -fPIC -march=native -mrtm
-DALLOW_EXPERIMENTAL_API -DALLOW_INTERNAL_API -Wno-format-truncation
-DVHOST_GCC_UNROLL_PRAGMA -fno-strict-aliasing -DVHOST_HAS_VDUSE
-DRTE_LOG_DEFAULT_LOGTYPE=lib.vhost -MD -MQ
lib/librte_vhost.a.p/vhost_virtio_net.c.o -MF
lib/librte_vhost.a.p/vhost_virtio_net.c.o.d -o
lib/librte_vhost.a.p/vhost_virtio_net.c.o -c
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c
In function ‘mbuf_to_desc’,
inlined from ‘vhost_enqueue_async_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1948:6,
inlined from ‘virtio_dev_rx_async_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1965:6,
inlined from ‘virtio_dev_rx_async_submit_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:2127:7:
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1230:18: error:
‘buf_vec[0].buf_addr’ may be used uninitialized
[-Werror=maybe-uninitialized]
1230 | buf_addr = buf_vec[vec_idx].buf_addr;
| ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c: In function
‘virtio_dev_rx_async_submit_packed’:
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1963:27: note:
‘buf_vec’ declared here
1963 | struct buf_vector buf_vec[BUF_VECTOR_MAX];
| ^~~~~~~
In function ‘mbuf_to_desc’,
inlined from ‘vhost_enqueue_async_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1948:6,
inlined from ‘virtio_dev_rx_async_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1965:6,
inlined from ‘virtio_dev_rx_async_submit_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:2127:7:
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1231:18: error:
‘buf_vec[0].buf_iova’ may be used uninitialized
[-Werror=maybe-uninitialized]
1231 | buf_iova = buf_vec[vec_idx].buf_iova;
| ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c: In function
‘virtio_dev_rx_async_submit_packed’:
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1963:27: note:
‘buf_vec’ declared here
1963 | struct buf_vector buf_vec[BUF_VECTOR_MAX];
| ^~~~~~~
In function ‘mbuf_to_desc’,
inlined from ‘vhost_enqueue_async_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1948:6,
inlined from ‘virtio_dev_rx_async_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1965:6,
inlined from ‘virtio_dev_rx_async_submit_packed’ at
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:2127:7:
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1232:35: error:
‘buf_vec[0].buf_len’ may be used uninitialized
[-Werror=maybe-uninitialized]
1232 | buf_len = buf_vec[vec_idx].buf_len;
| ~~~~~~~~~~~~~~~~^~~~~~~~
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c: In function
‘virtio_dev_rx_async_submit_packed’:
../../../git/pub/dpdk.org/main/lib/vhost/virtio_net.c:1963:27: note:
‘buf_vec’ declared here
1963 | struct buf_vector buf_vec[BUF_VECTOR_MAX];
| ^~~~~~~
cc1: all warnings being treated as errors
ninja: build stopped: subcommand failed.
I had a look at the vhost library and I think the compiler thinks size may be 0.
Changing the loop on size with a do { } while (size > 0); resolves the warning.
I can post a change for this, as we hit a similar issue in the past
and the code does not make sense comparing size on the first iteration
of this loop.
However, I am a bit puzzled why the prefetch change makes the compiler
consider this loop differently.
We have the same constructs everywhere in this library and x86_64
builds are fine...
--
David Marchand
