On Tue, Feb 07, 2017 at 02:43:17PM +0800, Eli Qiao wrote:
On Tuesday, 7 February 2017 at 12:11 AM, Daniel P. Berrange wrote:
On Mon, Feb 06, 2017 at 10:23:36AM +0800, Eli Qiao wrote:
This patch adds some utils struct and functions to expose resctrl information.
virResCtrlAvailable: If resctrl interface exist on host virResCtrlGet: get specify type resource contral information virResCtrlInit: initialize resctrl struct from the host's sys fs. ResCtrlAll[]: an array to maintain resource control information.
Signed-off-by: Eli Qiao <liyong.qiao@intel.com (mailto:liyong.qiao@intel.com)> --- +}; + + +typedef struct _virResCacheBank virResCacheBank; +typedef virResCacheBank *virResCacheBankPtr; +struct _virResCacheBank { + unsigned int host_id; + unsigned long long cache_size; + unsigned long long cache_left; + unsigned long long cache_min; + virBitmapPtr cpu_mask; +};
+typedef struct _virResCtrl virResCtrl; +typedef virResCtrl *virResCtrlPtr; +struct _virResCtrl { + bool enabled; + const char *name; + int num_closid; + int cbm_len; + int min_cbm_bits; + const char* cache_level; + int num_banks; + virResCacheBankPtr cache_banks; +};
Can any of these fields change at runtime, or are they all immutable once populated.
Only cache_banks will be change at runtime, such as cache_left on each socket will be updated if libvirt allocates cache to domains.
Ok, so the API is returning a direct point to the virResCtrlPtr struct and there's no locking here. So if cache_banks struct contents changes while some caller is reading the virResCtrlPtr struct we have race problems. I'd suggest that best option is probably to take the mutable cache_left field *out* of the struct. That lets the callers treat the entire struct as immutable. Then add a separate API to explicitly query the cache_left value - only that api needs to do locking to return a consistent point-in-time view of the cache_left value. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|