svn commit: r191405 - in head/sys: amd64/amd64 i386/i386

Thu Apr 23 11:55:55 UTC 2009

On Wed, 22 Apr 2009, John Baldwin wrote:

>  Adjust the way we number CPUs on x86 so that we attempt to "group" all
>  logical CPUs in a package.  We do this by numbering the non-boot CPUs
>  by starting with the first CPU whose APIC ID is after the boot CPU and
>  wrapping back around to APIC ID 0 if needed rather than always starting
>  at APIC ID 0.  While here, adjust the cpu_mp_announce() routine to list
>  CPUs based on the mapping established by assign_cpu_ids() rather than
>  making assumptions about the algorithm assign_cpu_ids() uses.

Something we'd like to be able to do in the fairly near future is assign work 
from one thread/core to another thread/core that is cache-wise "close" to the 
current one.  For example, if we take a cacheline miss on an mbuf head and the 
first line of a packet's data on one CPU, and want to hand it off to another 
CPU for further processing, trying to send it somewhere where it's already 
quite close, cache-wise, might well be beneficial.  Likewise, sending it to 
another thread or core that is cache-wise close on the lock protecting the 
queue used to pass it between CPUs, would also be nice.

Do you have any ideas about ways to usefully represent and manage concepts 
like "pick a close CPU" or "the set of CPUs that are close"?  For example, if 
I have available a flow identifier, hashing to one of a set of available CPUs 
is easy, but what would you suggest as an efficient representation to hash 
from a set of close available CPUs rather than the entire pool?

Robert N M Watson
Computer Laboratory
University of Cambridge

>
>  MFC after:	1 month
>
> Modified:
>  head/sys/amd64/amd64/mp_machdep.c
>  head/sys/i386/i386/mp_machdep.c
>
> Modified: head/sys/amd64/amd64/mp_machdep.c
> ==============================================================================
> --- head/sys/amd64/amd64/mp_machdep.c	Wed Apr 22 20:58:23 2009	(r191404)
> +++ head/sys/amd64/amd64/mp_machdep.c	Wed Apr 22 21:40:37 2009	(r191405)
> @@ -354,8 +354,6 @@ cpu_mp_start(void)
> 	} else
> 		KASSERT(boot_cpu_id == PCPU_GET(apic_id),
> 		    ("BSP's APIC ID doesn't match boot_cpu_id"));
> -	cpu_apic_ids[0] = boot_cpu_id;
> -	apic_cpuids[boot_cpu_id] = 0;
>
> 	/* Setup the initial logical CPUs info. */
> 	logical_cpus = logical_cpus_mask = 0;
> @@ -418,28 +416,30 @@ cpu_mp_start(void)
> void
> cpu_mp_announce(void)
> {
> -	int i, x;
> 	const char *hyperthread;
> +	int i;
>
> -	/* List CPUs */
> +	/* List active CPUs first. */
> 	printf(" cpu0 (BSP): APIC ID: %2d\n", boot_cpu_id);
> -	for (i = 1, x = 0; x <= MAX_APIC_ID; x++) {
> -		if (!cpu_info[x].cpu_present || cpu_info[x].cpu_bsp)
> +	for (i = 1; i < mp_ncpus; i++) {
> +		if (cpu_info[cpu_apic_ids[i]].cpu_hyperthread)
> +			hyperthread = "/HT";
> +		else
> +			hyperthread = "";
> +		printf(" cpu%d (AP%s): APIC ID: %2d\n", i, hyperthread,
> +		    cpu_apic_ids[i]);
> +	}
> +
> +	/* List disabled CPUs last. */
> +	for (i = 0; i <= MAX_APIC_ID; i++) {
> +		if (!cpu_info[i].cpu_present || !cpu_info[i].cpu_disabled)
> 			continue;
> -		if (cpu_info[x].cpu_hyperthread) {
> +		if (cpu_info[i].cpu_hyperthread)
> 			hyperthread = "/HT";
> -		} else {
> +		else
> 			hyperthread = "";
> -		}
> -		if (cpu_info[x].cpu_disabled)
> -			printf("  cpu (AP%s): APIC ID: %2d (disabled)\n",
> -			    hyperthread, x);
> -		else {
> -			KASSERT(i < mp_ncpus,
> -			    ("mp_ncpus and actual cpus are out of whack"));
> -			printf(" cpu%d (AP%s): APIC ID: %2d\n", i++,
> -			    hyperthread, x);
> -		}
> +		printf("  cpu (AP%s): APIC ID: %2d (disabled)\n", hyperthread,
> +		    i);
> 	}
> }
>
> @@ -693,11 +693,19 @@ assign_cpu_ids(void)
>
> 	/*
> 	 * Assign CPU IDs to local APIC IDs and disable any CPUs
> -	 * beyond MAXCPU.  CPU 0 has already been assigned to the BSP,
> -	 * so we only have to assign IDs for APs.
> +	 * beyond MAXCPU.  CPU 0 is always assigned to the BSP.
> +	 *
> +	 * To minimize confusion for userland, we attempt to number
> +	 * CPUs such that all threads and cores in a package are
> +	 * grouped together.  For now we assume that the BSP is always
> +	 * the first thread in a package and just start adding APs
> +	 * starting with the BSP's APIC ID.
> 	 */
> 	mp_ncpus = 1;
> -	for (i = 0; i <= MAX_APIC_ID; i++) {
> +	cpu_apic_ids[0] = boot_cpu_id;
> +	apic_cpuids[boot_cpu_id] = 0;
> +	for (i = boot_cpu_id + 1; i != boot_cpu_id;
> +	     i == MAX_APIC_ID ? i = 0 : i++) {
> 		if (!cpu_info[i].cpu_present || cpu_info[i].cpu_bsp ||
> 		    cpu_info[i].cpu_disabled)
> 			continue;
>
> Modified: head/sys/i386/i386/mp_machdep.c
> ==============================================================================
> --- head/sys/i386/i386/mp_machdep.c	Wed Apr 22 20:58:23 2009	(r191404)
> +++ head/sys/i386/i386/mp_machdep.c	Wed Apr 22 21:40:37 2009	(r191405)
> @@ -398,8 +398,6 @@ cpu_mp_start(void)
> 	} else
> 		KASSERT(boot_cpu_id == PCPU_GET(apic_id),
> 		    ("BSP's APIC ID doesn't match boot_cpu_id"));
> -	cpu_apic_ids[0] = boot_cpu_id;
> -	apic_cpuids[boot_cpu_id] = 0;
>
> 	/* Setup the initial logical CPUs info. */
> 	logical_cpus = logical_cpus_mask = 0;
> @@ -462,28 +460,30 @@ cpu_mp_start(void)
> void
> cpu_mp_announce(void)
> {
> -	int i, x;
> 	const char *hyperthread;
> +	int i;
>
> -	/* List CPUs */
> +	/* List active CPUs first. */
> 	printf(" cpu0 (BSP): APIC ID: %2d\n", boot_cpu_id);
> -	for (i = 1, x = 0; x <= MAX_APIC_ID; x++) {
> -		if (!cpu_info[x].cpu_present || cpu_info[x].cpu_bsp)
> +	for (i = 1; i < mp_ncpus; i++) {
> +		if (cpu_info[cpu_apic_ids[i]].cpu_hyperthread)
> +			hyperthread = "/HT";
> +		else
> +			hyperthread = "";
> +		printf(" cpu%d (AP%s): APIC ID: %2d\n", i, hyperthread,
> +		    cpu_apic_ids[i]);
> +	}
> +
> +	/* List disabled CPUs last. */
> +	for (i = 0; i <= MAX_APIC_ID; i++) {
> +		if (!cpu_info[i].cpu_present || !cpu_info[i].cpu_disabled)
> 			continue;
> -		if (cpu_info[x].cpu_hyperthread) {
> +		if (cpu_info[i].cpu_hyperthread)
> 			hyperthread = "/HT";
> -		} else {
> +		else
> 			hyperthread = "";
> -		}
> -		if (cpu_info[x].cpu_disabled)
> -			printf("  cpu (AP%s): APIC ID: %2d (disabled)\n",
> -			    hyperthread, x);
> -		else {
> -			KASSERT(i < mp_ncpus,
> -			    ("mp_ncpus and actual cpus are out of whack"));
> -			printf(" cpu%d (AP%s): APIC ID: %2d\n", i++,
> -			    hyperthread, x);
> -		}
> +		printf("  cpu (AP%s): APIC ID: %2d (disabled)\n", hyperthread,
> +		    i);
> 	}
> }
>
> @@ -722,11 +722,19 @@ assign_cpu_ids(void)
>
> 	/*
> 	 * Assign CPU IDs to local APIC IDs and disable any CPUs
> -	 * beyond MAXCPU.  CPU 0 has already been assigned to the BSP,
> -	 * so we only have to assign IDs for APs.
> +	 * beyond MAXCPU.  CPU 0 is always assigned to the BSP.
> +	 *
> +	 * To minimize confusion for userland, we attempt to number
> +	 * CPUs such that all threads and cores in a package are
> +	 * grouped together.  For now we assume that the BSP is always
> +	 * the first thread in a package and just start adding APs
> +	 * starting with the BSP's APIC ID.
> 	 */
> 	mp_ncpus = 1;
> -	for (i = 0; i <= MAX_APIC_ID; i++) {
> +	cpu_apic_ids[0] = boot_cpu_id;
> +	apic_cpuids[boot_cpu_id] = 0;
> +	for (i = boot_cpu_id + 1; i != boot_cpu_id;
> +	     i == MAX_APIC_ID ? i = 0 : i++) {
> 		if (!cpu_info[i].cpu_present || cpu_info[i].cpu_bsp ||
> 		    cpu_info[i].cpu_disabled)
> 			continue;
>