Message ID | 1330102654-2474-1-git-send-email-santoshprasadnayak@gmail.com |
---|---|
State | Rejected, archived |
Delegated to: | David Miller |
Headers | show |
Am 24.02.2012 17:57, schrieb santosh nayak: > From: Santosh Nayak <santoshprasadnayak@gmail.com> > > Sparse is giving the following warning: > "warning: dubious: x | !y" > > "enic_are_pp_different" is static and expected to return true or false. > Logical or is indended here. With logical or, in best case, execution will be > faster because if leftmost operand is true then no need to check other operands. > > Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com> > --- > drivers/net/ethernet/cisco/enic/enic_pp.c | 8 ++++---- > 1 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/ethernet/cisco/enic/enic_pp.c b/drivers/net/ethernet/cisco/enic/enic_pp.c > index dafea1e..3a6de22 100644 > --- a/drivers/net/ethernet/cisco/enic/enic_pp.c > +++ b/drivers/net/ethernet/cisco/enic/enic_pp.c > @@ -159,10 +159,10 @@ static int enic_unset_port_profile(struct enic *enic, int vf) > static int enic_are_pp_different(struct enic_port_profile *pp1, > struct enic_port_profile *pp2) > { > - return strcmp(pp1->name, pp2->name) | !!memcmp(pp1->instance_uuid,pp2->instance_uuid, PORT_UUID_MAX) | > - !!memcmp(pp1->host_uuid, pp2->host_uuid, PORT_UUID_MAX) | > - !!memcmp(pp1->mac_addr, pp2->mac_addr, ETH_ALEN); > + return strcmp(pp1->name, pp2->name) || !!memcmp(pp1->instance_uuid,pp2->instance_uuid, PORT_UUID_MAX) || > + !!memcmp(pp1->host_uuid, pp2->host_uuid, PORT_UUID_MAX) || > + !!memcmp(pp1->mac_addr, pp2->mac_addr, ETH_ALEN); > } > to be fair, this is next to unreadable (not your fault of cause). Instead of squeezing this into a one statement i would suggest more statements. just my 2 cents, re, wh > static int enic_pp_preassociate(struct enic *enic, int vf, -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, 2012-02-24 at 22:27 +0530, santosh nayak wrote: > From: Santosh Nayak <santoshprasadnayak@gmail.com> > > Sparse is giving the following warning: > "warning: dubious: x | !y" > > "enic_are_pp_different" is static and expected to return true or false. > Logical or is indended here. With logical or, in best case, execution will be > faster because if leftmost operand is true then no need to check other operands. The shortcut behaviour of logical-or means more conditional jumps to be predicted and more potential for pipeline stalls. So bitwise-or can in some cases be more efficient. But this function appears to be control-path code where micro-optimisation just doesn't matter. Use of logical-or can be justified purely on the grounds of clarity. Ben. > Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com> > --- > drivers/net/ethernet/cisco/enic/enic_pp.c | 8 ++++---- > 1 files changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/ethernet/cisco/enic/enic_pp.c b/drivers/net/ethernet/cisco/enic/enic_pp.c > index dafea1e..3a6de22 100644 > --- a/drivers/net/ethernet/cisco/enic/enic_pp.c > +++ b/drivers/net/ethernet/cisco/enic/enic_pp.c > @@ -159,10 +159,10 @@ static int enic_unset_port_profile(struct enic *enic, int vf) > static int enic_are_pp_different(struct enic_port_profile *pp1, > struct enic_port_profile *pp2) > { > - return strcmp(pp1->name, pp2->name) | !!memcmp(pp1->instance_uuid, > - pp2->instance_uuid, PORT_UUID_MAX) | > - !!memcmp(pp1->host_uuid, pp2->host_uuid, PORT_UUID_MAX) | > - !!memcmp(pp1->mac_addr, pp2->mac_addr, ETH_ALEN); > + return strcmp(pp1->name, pp2->name) || !!memcmp(pp1->instance_uuid, > + pp2->instance_uuid, PORT_UUID_MAX) || > + !!memcmp(pp1->host_uuid, pp2->host_uuid, PORT_UUID_MAX) || > + !!memcmp(pp1->mac_addr, pp2->mac_addr, ETH_ALEN); > } > > static int enic_pp_preassociate(struct enic *enic, int vf,
From: santosh nayak <santoshprasadnayak@gmail.com> Date: Fri, 24 Feb 2012 22:27:34 +0530 > From: Santosh Nayak <santoshprasadnayak@gmail.com> > > Sparse is giving the following warning: > "warning: dubious: x | !y" > > "enic_are_pp_different" is static and expected to return true or false. > Logical or is indended here. With logical or, in best case, execution will be > faster because if leftmost operand is true then no need to check other operands. > > Signed-off-by: Santosh Nayak <santoshprasadnayak@gmail.com> As others have explained, this code is intentional. It's faster because the resulting code has less branches and therefore less potential branch mispredictions. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/net/ethernet/cisco/enic/enic_pp.c b/drivers/net/ethernet/cisco/enic/enic_pp.c index dafea1e..3a6de22 100644 --- a/drivers/net/ethernet/cisco/enic/enic_pp.c +++ b/drivers/net/ethernet/cisco/enic/enic_pp.c @@ -159,10 +159,10 @@ static int enic_unset_port_profile(struct enic *enic, int vf) static int enic_are_pp_different(struct enic_port_profile *pp1, struct enic_port_profile *pp2) { - return strcmp(pp1->name, pp2->name) | !!memcmp(pp1->instance_uuid, - pp2->instance_uuid, PORT_UUID_MAX) | - !!memcmp(pp1->host_uuid, pp2->host_uuid, PORT_UUID_MAX) | - !!memcmp(pp1->mac_addr, pp2->mac_addr, ETH_ALEN); + return strcmp(pp1->name, pp2->name) || !!memcmp(pp1->instance_uuid, + pp2->instance_uuid, PORT_UUID_MAX) || + !!memcmp(pp1->host_uuid, pp2->host_uuid, PORT_UUID_MAX) || + !!memcmp(pp1->mac_addr, pp2->mac_addr, ETH_ALEN); } static int enic_pp_preassociate(struct enic *enic, int vf,