[PATCH] net/qede: reduce the optimization level

[PATCH] net/qede: reduce the optimization level

[Thierry Herbelot]

The qede PMD stopped working under Ubuntu-24.04 (using gcc-13) when
compiled with -O3 (default level for all DPDK code). A bug is opened
for this issue (see Link).

A first workaround is to just disable all optimizations (-O0), which
restores packet Rx with Qlogic NICs. However, the performance impact
is not acceptable (around 50% drop).

A better compromise is to use -O1 for the qede PMD:
- there is some perf impact,
- but the PMD is working as expected (packets are correctly received).

When compiling with both -O2 and -O3 and gcc-13, there is no packet
reception when using the qede PMD. The root cause could be missing
'volatile' keywords or missing memory barriers in the qede PMD code.

Link: https://bugs.dpdk.org/show_bug.cgi?id=1379
Signed-off-by: Thierry Herbelot <thierry.herbelot@6wind.com>
---
 drivers/net/qede/base/meson.build | 1 +
 drivers/net/qede/meson.build      | 1 +
 2 files changed, 2 insertions(+)

diff --git a/drivers/net/qede/base/meson.build b/drivers/net/qede/base/meson.build
index a6dad3ec7bcc..6c8800a3f48f 100644
--- a/drivers/net/qede/base/meson.build
+++ b/drivers/net/qede/base/meson.build
@@ -55,3 +55,4 @@ foreach flag: error_cflags
         base_cflags += flag
     endif
 endforeach
+base_cflags += '-O1'
diff --git a/drivers/net/qede/meson.build b/drivers/net/qede/meson.build
index e1b21d6ff5cd..3c2a5205732a 100644
--- a/drivers/net/qede/meson.build
+++ b/drivers/net/qede/meson.build
@@ -22,3 +22,4 @@ sources = files(
 if cc.has_argument('-Wno-format-nonliteral')
     cflags += '-Wno-format-nonliteral'
 endif
+cflags += '-O1'
-- 
2.39.2

Re: [PATCH] net/qede: reduce the optimization level

[Stephen Hemminger]

On Wed,  3 Sep 2025 13:32:52 +0200
Thierry Herbelot <thierry.herbelot@6wind.com> wrote:

> The qede PMD stopped working under Ubuntu-24.04 (using gcc-13) when
> compiled with -O3 (default level for all DPDK code). A bug is opened
> for this issue (see Link).
> 
> A first workaround is to just disable all optimizations (-O0), which
> restores packet Rx with Qlogic NICs. However, the performance impact
> is not acceptable (around 50% drop).
> 
> A better compromise is to use -O1 for the qede PMD:
> - there is some perf impact,
> - but the PMD is working as expected (packets are correctly received).
> 
> When compiling with both -O2 and -O3 and gcc-13, there is no packet
> reception when using the qede PMD. The root cause could be missing
> 'volatile' keywords or missing memory barriers in the qede PMD code.
> 
> Link: https://bugs.dpdk.org/show_bug.cgi?id=1379
> Signed-off-by: Thierry Herbelot <thierry.herbelot@6wind.com>

Since GCC 14 and 15 are available do they fix the problem?
If so, the the hack should be limited to Gcc 13 and with
more complete comment.

[V2] net/qede: reduce the optimization level for gcc > 11

[Thierry Herbelot]

The qede PMD stopped working under Ubuntu-24.04 (using gcc-13) when
compiled with -O3 (default level for all DPDK code). A bug is opened
for this issue (see Link). The same issue is also seen with gcc-12
and gcc-14.

A first workaround is to just disable all optimizations (-O0), which
restores packet Rx with Qlogic NICs. However, the performance impact
is not acceptable (around 50% drop).

A better compromise is to use -O1 for the qede PMD:
- there is some perf impact,
- but the PMD is working as expected (packets are correctly received).

When compiling with both -O2 and -O3 and gcc > 11, there is no packet
reception when using the qede PMD. The root cause could be missing
'volatile' keywords or missing memory barriers in the qede PMD code.

Link: https://bugs.dpdk.org/show_bug.cgi?id=1379
Signed-off-by: Thierry Herbelot <thierry.herbelot@6wind.com>
---
V2: be more precise when dropping optimization level (only for gcc > 11)
---
 drivers/net/qede/base/meson.build | 4 ++++
 drivers/net/qede/meson.build      | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/net/qede/base/meson.build b/drivers/net/qede/base/meson.build
index a6dad3ec7bcc..130835cc31b1 100644
--- a/drivers/net/qede/base/meson.build
+++ b/drivers/net/qede/base/meson.build
@@ -55,3 +55,7 @@ foreach flag: error_cflags
         base_cflags += flag
     endif
 endforeach
+# no packet Rx with gcc > 11 with compiling with default -O3 or -O2
+if (cc.get_id() == 'gcc' and cc.version().version_compare('>11.0'))
+    base_cflags += '-O1'
+endif
diff --git a/drivers/net/qede/meson.build b/drivers/net/qede/meson.build
index e1b21d6ff5cd..e4268883ff93 100644
--- a/drivers/net/qede/meson.build
+++ b/drivers/net/qede/meson.build
@@ -22,3 +22,7 @@ sources = files(
 if cc.has_argument('-Wno-format-nonliteral')
     cflags += '-Wno-format-nonliteral'
 endif
+# no packet Rx with gcc > 11 with compiling with default -O3 or -O2
+if (cc.get_id() == 'gcc' and cc.version().version_compare('>11.0'))
+    cflags += '-O1'
+endif
-- 
2.39.2

Re: [V2] net/qede: reduce the optimization level for gcc > 11

[Stephen Hemminger]

On Mon,  8 Sep 2025 09:04:13 +0200
Thierry Herbelot <thierry.herbelot@6wind.com> wrote:

> +# no packet Rx with gcc > 11 with compiling with default -O3 or -O2
> +if (cc.get_id() == 'gcc' and cc.version().version_compare('>11.0'))
> +    base_cflags += '-O1'
> +endif

Did you test with Gcc 14 and 15, it may be the bug is already fixed.

Re: [V2] net/qede: reduce the optimization level for gcc > 11

[Thierry Herbelot]

On 9/8/25 21:59, Stephen Hemminger wrote:
> On Mon,  8 Sep 2025 09:04:13 +0200
> Thierry Herbelot <thierry.herbelot@6wind.com> wrote:
> 
>> +# no packet Rx with gcc > 11 with compiling with default -O3 or -O2
>> +if (cc.get_id() == 'gcc' and cc.version().version_compare('>11.0'))
>> +    base_cflags += '-O1'
>> +endif
> 
> Did you test with Gcc 14 and 15, it may be the bug is already fixed.

As said in the commit log:

"The same issue is also seen with gcc-12 and gcc-14."

I did not test with gcc-15.

The issue is not seen with clang20 (qede PMD compiled with -O3 works as 
expected).

	Best regards

	Thierry

-- 
Thierry Herbelot
CSE - Titulaire au collège Cadres
Senior Software Engineer
http://www.6wind.com/

Follow us:
https://www.linkedin.com/company/6wind/
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https://www.youtube.com/user/6windsoftware

[V3] net/qede: reduce the optimization level for gcc > 11

[Thierry Herbelot]

The qede PMD stopped working under Ubuntu-24.04 (using gcc-13) when
compiled with -O3 (default level for all DPDK code). A bug is opened
for this issue (see Link). The same issue is also seen with gcc-12
and gcc-14. The issue is not seen with clang-20.

A first workaround is to just disable all optimizations (-O0), which
restores packet Rx with Qlogic NICs. However, the performance impact
is not acceptable (around 50% drop).

A better compromise is to use -O1 for the qede PMD:
- there is some perf impact,
- but the PMD is working as expected (packets are correctly received).

When compiling with both -O2 and -O3 and gcc > 11, there is no packet
reception when using the qede PMD. The root cause could be missing
'volatile' keywords or missing memory barriers in the qede PMD code.

Link: https://bugs.dpdk.org/show_bug.cgi?id=1379
Signed-off-by: Thierry Herbelot <thierry.herbelot@6wind.com>
---
V2: be more precise when dropping optimization level (only for gcc > 11)
V3: even more precise: the issue appears with gcc-12
---
 drivers/net/qede/base/meson.build | 4 ++++
 drivers/net/qede/meson.build      | 4 ++++
 2 files changed, 8 insertions(+)

diff --git a/drivers/net/qede/base/meson.build b/drivers/net/qede/base/meson.build
index a6dad3ec7bcc..acab6e8ac938 100644
--- a/drivers/net/qede/base/meson.build
+++ b/drivers/net/qede/base/meson.build
@@ -55,3 +55,7 @@ foreach flag: error_cflags
         base_cflags += flag
     endif
 endforeach
+# no packet Rx with gcc > 11 with compiling with default -O3 or -O2
+if (cc.get_id() == 'gcc' and cc.version().version_compare('>=12.0'))
+    base_cflags += '-O1'
+endif
diff --git a/drivers/net/qede/meson.build b/drivers/net/qede/meson.build
index e1b21d6ff5cd..86c3503a82f6 100644
--- a/drivers/net/qede/meson.build
+++ b/drivers/net/qede/meson.build
@@ -22,3 +22,7 @@ sources = files(
 if cc.has_argument('-Wno-format-nonliteral')
     cflags += '-Wno-format-nonliteral'
 endif
+# no packet Rx with gcc > 11 with compiling with default -O3 or -O2
+if (cc.get_id() == 'gcc' and cc.version().version_compare('>=12.0'))
+    cflags += '-O1'
+endif
-- 
2.39.2

Re: [V3] net/qede: reduce the optimization level for gcc > 11

[Stephen Hemminger]

On Tue,  9 Sep 2025 07:40:23 +0200
Thierry Herbelot <thierry.herbelot@6wind.com> wrote:

> The qede PMD stopped working under Ubuntu-24.04 (using gcc-13) when
> compiled with -O3 (default level for all DPDK code). A bug is opened
> for this issue (see Link). The same issue is also seen with gcc-12
> and gcc-14. The issue is not seen with clang-20.
> 
> A first workaround is to just disable all optimizations (-O0), which
> restores packet Rx with Qlogic NICs. However, the performance impact
> is not acceptable (around 50% drop).
> 
> A better compromise is to use -O1 for the qede PMD:
> - there is some perf impact,
> - but the PMD is working as expected (packets are correctly received).
> 
> When compiling with both -O2 and -O3 and gcc > 11, there is no packet
> reception when using the qede PMD. The root cause could be missing
> 'volatile' keywords or missing memory barriers in the qede PMD code.
> 
> Link: https://bugs.dpdk.org/show_bug.cgi?id=1379
> Signed-off-by: Thierry Herbelot <thierry.herbelot@6wind.com>

Which rx_burst gets used on that hardware?

Is there any indication of errors (like rx_mbuf_alloc_failed) in the stats.

The driver does not appear to have any write barrier after updating the consumed packets.

Would this help?
diff --git a/drivers/net/qede/qede_rxtx.c b/drivers/net/qede/qede_rxtx.c
index 25e28fd9f6..1b5109d966 100644
--- a/drivers/net/qede/qede_rxtx.c
+++ b/drivers/net/qede/qede_rxtx.c
@@ -1295,6 +1295,8 @@ static inline void qede_rx_bd_ring_consume(struct qede_rx_queue *rxq)
 {
        ecore_chain_consume(&rxq->rx_bd_ring);
        rxq->sw_rx_cons++;
+
+       rte_wmb();
 }