| Message ID | Y+I7/QpQYjBXutLf@ubun2204.myguest.virtualbox.org (mailing list archive) |
|---|---|
| State | Rejected |
| Headers | show |
| Series | scsi: qla1280: Replace arithmetic addition by bitwise OR | expand |
On 2/7/23 03:54, Deepak R Varma wrote: > When adding two bit-field mask values, an OR operation offers higher > performance over an arithmetic operation. So, convert such addition to > an OR based expression. Where is the evidence that supports this claim? On the following page I read that there is no performance difference when using a modern CPU: https://cs.stackexchange.com/questions/75811/why-is-addition-as-fast-as-bit-wise-operations-in-modern-processors > Issue identified using orplus.cocci semantic patch script. Where is that script located? Can it be deleted such that submission of patches similar to this patch stops? Thanks, Bart.
On Sat, Feb 11, 2023 at 03:25:03PM -0800, Bart Van Assche wrote: > On 2/7/23 03:54, Deepak R Varma wrote: > > When adding two bit-field mask values, an OR operation offers higher > > performance over an arithmetic operation. So, convert such addition to > > an OR based expression. > > Where is the evidence that supports this claim? On the following page I read > that there is no performance difference when using a modern CPU: https://cs.stackexchange.com/questions/75811/why-is-addition-as-fast-as-bit-wise-operations-in-modern-processors > Hello Bart, You are correct. Modern CPU designs have improved addition and the performance is at par with the bitwise operation. The document I had read earlier mentioned a performance improvement for old CPUs and microprocessors, which today is not the case. Thank you for sharing the link. > > Issue identified using orplus.cocci semantic patch script. > > Where is that script located? Can it be deleted such that submission of > patches similar to this patch stops? I have added Julia to this email to understand how to best use this semantic patch. I already discussed with her on improving the Semantic patch such that it doesn't suggest making change when constants are involved. Thank you, ./drv > > Thanks, > > Bart.
On Sun, 12 Feb 2023, Deepak R Varma wrote: > On Sat, Feb 11, 2023 at 03:25:03PM -0800, Bart Van Assche wrote: > > On 2/7/23 03:54, Deepak R Varma wrote: > > > When adding two bit-field mask values, an OR operation offers higher > > > performance over an arithmetic operation. So, convert such addition to > > > an OR based expression. > > > > Where is the evidence that supports this claim? On the following page I read > > that there is no performance difference when using a modern CPU: https://cs.stackexchange.com/questions/75811/why-is-addition-as-fast-as-bit-wise-operations-in-modern-processors > > > > Hello Bart, > You are correct. Modern CPU designs have improved addition and the performance > is at par with the bitwise operation. The document I had read earlier mentioned > a performance improvement for old CPUs and microprocessors, which today is not > the case. Thank you for sharing the link. > > > > Issue identified using orplus.cocci semantic patch script. > > > > Where is that script located? Can it be deleted such that submission of > > patches similar to this patch stops? > > I have added Julia to this email to understand how to best use this semantic > patch. I already discussed with her on improving the Semantic patch such that it > doesn't suggest making change when constants are involved. FWIW, the semantic patch was never motivated by efficiency, but rather with the goal of making the code more understandable. julia
On Sun, Feb 12, 2023 at 04:11:58PM +0100, Julia Lawall wrote: > > > On Sun, 12 Feb 2023, Deepak R Varma wrote: > > > On Sat, Feb 11, 2023 at 03:25:03PM -0800, Bart Van Assche wrote: > > > On 2/7/23 03:54, Deepak R Varma wrote: > > > > When adding two bit-field mask values, an OR operation offers higher > > > > performance over an arithmetic operation. So, convert such addition to > > > > an OR based expression. > > > > > > Where is the evidence that supports this claim? On the following page I read > > > that there is no performance difference when using a modern CPU: https://cs.stackexchange.com/questions/75811/why-is-addition-as-fast-as-bit-wise-operations-in-modern-processors > > > > > > > Hello Bart, > > You are correct. Modern CPU designs have improved addition and the performance > > is at par with the bitwise operation. The document I had read earlier mentioned > > a performance improvement for old CPUs and microprocessors, which today is not > > the case. Thank you for sharing the link. > > > > > > Issue identified using orplus.cocci semantic patch script. > > > > > > Where is that script located? Can it be deleted such that submission of > > > patches similar to this patch stops? > > > > I have added Julia to this email to understand how to best use this semantic > > patch. I already discussed with her on improving the Semantic patch such that it > > doesn't suggest making change when constants are involved. > > FWIW, the semantic patch was never motivated by efficiency, but rather > with the goal of making the code more understandable. I think my interpretation of the patch log for [1] was not accurate. The line "Running time is divided by 3 ..." made me believe OR'ing would replace "F+A+R" instructions by a single operation. My bad. [1] https://lore.kernel.org/all/alpine.DEB.2.20.1711130649370.2483@hadrien/ > > julia
On Sun, 12 Feb 2023, Deepak R Varma wrote: > On Sun, Feb 12, 2023 at 04:11:58PM +0100, Julia Lawall wrote: > > > > > > On Sun, 12 Feb 2023, Deepak R Varma wrote: > > > > > On Sat, Feb 11, 2023 at 03:25:03PM -0800, Bart Van Assche wrote: > > > > On 2/7/23 03:54, Deepak R Varma wrote: > > > > > When adding two bit-field mask values, an OR operation offers higher > > > > > performance over an arithmetic operation. So, convert such addition to > > > > > an OR based expression. > > > > > > > > Where is the evidence that supports this claim? On the following page I read > > > > that there is no performance difference when using a modern CPU: https://cs.stackexchange.com/questions/75811/why-is-addition-as-fast-as-bit-wise-operations-in-modern-processors > > > > > > > > > > Hello Bart, > > > You are correct. Modern CPU designs have improved addition and the performance > > > is at par with the bitwise operation. The document I had read earlier mentioned > > > a performance improvement for old CPUs and microprocessors, which today is not > > > the case. Thank you for sharing the link. > > > > > > > > Issue identified using orplus.cocci semantic patch script. > > > > > > > > Where is that script located? Can it be deleted such that submission of > > > > patches similar to this patch stops? > > > > > > I have added Julia to this email to understand how to best use this semantic > > > patch. I already discussed with her on improving the Semantic patch such that it > > > doesn't suggest making change when constants are involved. > > > > FWIW, the semantic patch was never motivated by efficiency, but rather > > with the goal of making the code more understandable. > > I think my interpretation of the patch log for [1] was not accurate. The line > "Running time is divided by 3 ..." made me believe OR'ing would replace "F+A+R" > instructions by a single operation. My bad. Ah, interesting. I have no idea any more the running time of what. julia > > [1] https://lore.kernel.org/all/alpine.DEB.2.20.1711130649370.2483@hadrien/ > > > > > julia > > >
diff --git a/drivers/scsi/qla1280.c b/drivers/scsi/qla1280.c index 1e7f4d138e06..d806beb4ad1c 100644 --- a/drivers/scsi/qla1280.c +++ b/drivers/scsi/qla1280.c @@ -3709,7 +3709,7 @@ qla1280_error_entry(struct scsi_qla_host *ha, struct response *pkt, ha->outstanding_cmds[handle] = NULL; /* Bad payload or header */ - if (pkt->entry_status & (BIT_3 + BIT_2)) { + if (pkt->entry_status & (BIT_3 | BIT_2)) { /* Bad payload or header, set error status. */ /* CMD_RESULT(sp->cmd) = CS_BAD_PAYLOAD; */ CMD_RESULT(sp->cmd) = DID_ERROR << 16;
When adding two bit-field mask values, an OR operation offers higher performance over an arithmetic operation. So, convert such addition to an OR based expression. Issue identified using orplus.cocci semantic patch script. Signed-off-by: Deepak R Varma <drv@mailo.com> --- drivers/scsi/qla1280.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)