From: Ferruh Yigit <ferruh.yigit@intel.com>
To: Stephen Hemminger <stephen@networkplumber.org>
Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH] ixgbe: fix icc compile error
Date: Wed, 23 Mar 2016 21:26:36 +0000 [thread overview]
Message-ID: <56F30A0C.5010207@intel.com> (raw)
In-Reply-To: <20160323123525.09de2b2f@xeon-e3>
On 3/23/2016 7:35 PM, Stephen Hemminger wrote:
> On Wed, 23 Mar 2016 17:45:58 +0000
> Ferruh Yigit <ferruh.yigit@intel.com> wrote:
>
>> Fixes: 06554d381d97 ("ixgbe: speed up non-vector Tx")
>>
>> icc (icc (ICC) 16.0.1 20151021) is generating following compile error:
>> "
>> CC ixgbe_rxtx.o
>> .../drivers/net/ixgbe/ixgbe_rxtx.c(153): error #3656: variable
>> "free" may be used before its value is set
>> (nb_free > 0 && m->pool != free[0]->pool)) {
>> ^
>> "
>>
>> Indeed this is a false positive and code is correct.
>> "nb_free" check prevents the free[] access before its value set.
>>
>> But the patch is just for compiler to remove compiler error.
>>
>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
>> ---
>> drivers/net/ixgbe/ixgbe_rxtx.c | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
>> index ff6ddb8..ef1a26f 100644
>> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
>> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
>> @@ -128,7 +128,8 @@ ixgbe_tx_free_bufs(struct ixgbe_tx_queue *txq)
>> struct ixgbe_tx_entry *txep;
>> uint32_t status;
>> int i, nb_free = 0;
>> - struct rte_mbuf *m, *free[RTE_IXGBE_TX_MAX_FREE_BUF_SZ];
>> + struct rte_mbuf *m;
>> + struct rte_mbuf *free[RTE_IXGBE_TX_MAX_FREE_BUF_SZ] = {0};
>>
>> /* check DD bit on threshold descriptor */
>> status = txq->tx_ring[txq->tx_next_dd].wb.status;
>
> Although this fixes a compiler bug, it also introduces a performance hit.
> The initialization will generate a string instruct (rep; stosz) and this
> stalls the multi-execution unit on many Intel CPU's.
>
> Better to add a override to the Makefile (for icc only and with big comment).
>
Thank you for the comment. Konstantin also expressed similar performance
concern related this patch.
Nack for the patch, we will look for different solution.
Regards,
ferruh
next prev parent reply other threads:[~2016-03-23 21:26 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-23 17:45 Ferruh Yigit
2016-03-23 19:35 ` Stephen Hemminger
2016-03-23 21:26 ` Ferruh Yigit [this message]
2016-03-24 17:34 ` [dpdk-dev] [PATCH v2] ixgbe: disable icc compile warning Ferruh Yigit
2016-03-24 17:47 ` Ananyev, Konstantin
2016-03-25 13:57 ` Bruce Richardson
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